tell a loved one you want to be frozen upon death, and that you would like them to take responsibility for making sure this happens. This takes literally 30 seconds

...and they probably won't do it when the time comes to act.

The history of cryonics teaches us that, while people often contact cryonics companies to freeze their already or soon-to-be dead relatives on their own incentive, it is a much more common situation that the relatives of a person who has already completed all the paperwork and paid for the cryopreservation with their own money try to actively prevent the preservation.

Note also that the non-signed-up people's relatives come from a population many orders of magnitude larger than signed-up people's relatives.