Most people lack autonomy in their daily lives. Next to life itself, freedom is the most precious value; and most people’s lives are functionally devoid of it.
Most people have a very limited range of interests and possibilities for gratification. This problem cannot be fixed for most by giving them more money, or even more money and autonomy. Do that, and they will drown themselves in what they already have, or kill themselves with drugs.
The vast majority of people over 30 don’t feel well a significant fraction of the time.
They are losing their own youth and health and watching others suffer and die around them.
It should thus come as little surprise that our prisons are currently filled with a disproportionate number of people who are more intelligent than average and who lack the social coping skills to get on in society. They are also smart enough to know that many of the rules and orders given them are arbitrary and have no basis in reason beyond maintaining the status quo.
TL;DR cryonics is unpopular because only intelligent people can understand the science behind it or conceptually grasp the futurist reasons for perusing it. Further, most people, apparently especially intelligent people, are unhappy and see no point in extending or prolonging the downward trend that is their happiness.