A tiny fraction of their users paying upfront (remember opportunity cost of money) is hardly going to doom them to insolvency.
Look at this way - investors give money to a company now to receive money later. They risk capital now in exchange for future rewards. Lifetime subscribers pay a large fixed amount now to receive free service later. Same thing.
I’ve heard that people claim the moon landings were faked, but (until now?) I’d never heard anyone claiming the Martian rovers were faked.