There's a lot of arguing, of course, on if humans are rational, but this often mixes up two things: there's the "Von Neumann-Morgenstern utility function maximization" definition of "rational", and there's a hypothetical "rational" that a human could fulfill with constraints much more complicated than the classical approach, more in the direction of prospect theory, or Predictive Coding.
I think I regard the second definition as sufficiently not understood or defined that it isn't yet worth using in most conversation. It seems challenging, to say the least, to ask if humans are rational according to some definition which we clearly do not even know yet, let alone expect others to agree with.
Or it could be an intuitive usage and mean "(more) optimal". "Why don't more people do [thing that will improve their health]?"