Reading Mastodon and listening to podcasts it has become accepted truth that only subscription pricing makes software development sustainable. That having users pay once is irresponsible.

But the underlying fallacy is that every user should make you profit.

To be sustainable your users collectively need to pay you enough and with millions of future users it is very possible to just have income from new users.

You still want to cater to existing users. Their goodwill will bring in new users.