As an experiment, here's a thread for people to post about things they care about. Specifically, for things that are possible to contribute to, in some way, and preferably, to invite others to join.
Mine is buying and donating highschool textbooks to schools in the 'grey zone' of Ukraine (where the war kinda isn't fought, but few people would be surprised if it started.) I don't deliver them myself, though.
What's yours?
If I may take a stab at this: it's probably a combination of 1) Costs a lot 2) Benefit isn't expected for many decades 3) No guarantee that it would work
Anyone taking a heurisitc approach to reasoning about whether to sign up for cryonics rather than a probabilistic one ( which isn't irrational if you have no way to estimate the probabilities involved available to you ) could therefore easily evaluate it as not worth doing.
The religious might also see it as an attempt to cheat God, which rarely ends well in the mythology.