AGI is likely closer than an anti-aging intervention that adds decades discovered without AGI. I used to believe that AGI results in either death or approximately immediate perfect cure for aging and other forms of mortality (depending on how AI alignment and judgement of morality work out), and that is a reason to mostly ignore anti-aging. Recently I began to see less powerful/general (by design) AGI as a plausible way of controlling AI risk, that isn't easy to make more generally useful safely. If that works out, immediate cure for aging doesn't follow, even after AI risk is no longer imminent. This makes current anti-aging research not as pointless. (In one partial failure mode, with an anti-goodharting non-corrigible AI, straightforward AI development might even become permanently impossible, thwarted by the AGI that controls AI risk but can't be disabled. In that case any anti-aging must be developed "manually".)

I can only speak for my personal experience, but I think there's a significant minority of rationalists who care about preventing their own personal deaths a lot. I know because I've met them during my own process of figuring out what to do about death.

Personally, I video record my most of my life, plan to get cryopreserved (especially via the best methods available), am interested in and currently trying to pursue evidence-based strategies to slow aging, and try to avoid excess exposure to risk of injuries. There's not a lot more I can personally do to stop my own death besides these things, so oftentimes, I tend to just stop talking about it.

I'm pretty concerned, I'm trying to prevent the AI catastrophe happening that will likely kill me.

Also my rationalist housemate Daniel Filan often reminds me of his basic belief about how doing 30 mins of exercise a few times a week has an expected return of something like 10 hours of life or whatever. (I forget the details.) It definitely happens to me a bunch.

Also right now I'm pretty excited about figuring out more of the micromorts I spend on different things, and get used to calculating things with them (including diet, exercise, as well as things in the reference class of walking through shady places at night or driving without a seatbelt). Now that I've gotten lots of practice with microcovid estimates, I can do this sort of thing much easier.

I care about longevity; I donate to longevity research institutions. I also try to live healthily.

That said, I'm also in my early 30s. I just took an actuarial table and my rough probability distribution of when I expect transformative AI to be possible and calculated my probability of dying vs. my probability of seeing transformative AI, and ended up with 23% and 77%. So, like,  even if I'm totally selfish, on my beliefs it seems three times more important to do something about the Singularity than all-cause mortality.

This is less true the older someone is, of course.

Speculation here, but if we grant your premise, then the answer to your question might be something like:

Rationalists largely come from engineering backgrounds.  Rightly or wrongly, AI is mostly framed in an engineering context and mortality is mostly framed in the context of biologists and medical doctors.

That being said, I think it's really important to suss out if the premise of your question is correct.  If it is so, and the signals we are getting about AI risk organizations having almost too much cash, we should be directing some portion of our funding to organizations like SENS instead of AI risk.

There are plenty of people who have AGI timelines that suggest to them that either AGI will kill them before they reach their natural mortality or AGI will be powerful enough to prevent their natural mortality by that point. 

Even without having direct access to AGI new machine learning advances for protein folding and protein design might be more central to longevity than the research that's billed as longevity research.

That said, I do agree that anti-aging is an important topic. One problem of how people who prescribe to fight it often seem to be into seeking the key under the lightbulb.

The SENS paradigm seems insular to me. I don't have a charitable explanation of why fascia getting tenser as people age isn't on their list of aging damage. 

I think many MANY smart people realize something is very wrong.  There's been a LOT written about it, including much of the early LessWrong content.  

The way I see it, when we're talking about non-me humans, the vast majority of them will be replaced with people I probably like roughly the same amount, so my preference for longevity in general is mild.  There is a crisis coming in my own death, but I don't see much to do about it.

to notice something is very very wrong and take action.
...
understand this problem is solvable in principle

I do NOT think that the "and take action" part is trivial, nor that the problem is solvable in principle, certainly not with much likelihood of impacting current rationalists' lives.

In terms of "what can I do to increase the area under the curve of probability-weighted happiness and longevity", working on nearer-term issues has much higher expected value, IMO. 

The anti-aging field is going great as far as I can see, with billion-dollar investements happening regularly, clinical trials are ongoing and the field as a whole has started to attract the attention it deserves. I think rationalists are not especially worried because they (or rather, I do) believe that the problem is already well on its way to being solved. If we don't all die from misaligned AI / nuclear war / biological weapon  in the next 20 years, I don't think we'll have to worry about aging too much.

Mortality is a very old problem, and lots of smart people have spent lots of time thinking about it. Perhaps the best intervention anyone has come up with is harm reduction via acceptance. That's the approach I'm taking personally. Denial is popular, but isn't very rationalist and seems to lead to more overall suffering.

I'm not working on promoting this approach because it's literally thousand of years old and that's not a good personal fit. But I support and respect people who do.

I'm not sure everyone thinks death is bad. I mean, it's been a "feature" of being human since before there were humans and it has worked quite well so far to have a process of death. Messing with a working system is always a dangerous proposition, so I, personally, wonder if it is wise to remove that feature. Therefore, I do nothing about it (maybe I should be more active in opposition? I don't know).