When I first started keeping a calendar, in 2006, it was just an HTML table on my website:
Over time, I extended it to generate an iCal feed and wrote several commands to make it easier to add entries to the table (proc_schedule). I knew it was a peculiar way of doing things, but it met my needs and I didn't feel much reason to switch.
With covid, however, I have a lot more short social events. An hour to play One Night Ultimate Werewolf, half an hour to talk with someone about a question they have, an hour and a half of no-hands pair programming on the bucket brigade singing project. Now I care about invites, RSVPs, time zones, video calls, and notifications. Yes, perhaps I could have extended my program to have all of these features, but why?
I'm already familiar with Google calendar because we use it at work, and have now switched over to it for personal things as well. If you want to invite me to something, use my firstname.lastname@example.org address.
(The spirit of generating a calendar feed from an HTML table lives on, however, in proc_fr_schedule and proc_kf_schedule for the Free Raisins and Kingfisher. Hopefully, post covid, there will be gigs again.)