You can consider using flagship instance as a way to fund the development. It's not like they force you to use flagship instance.

There always third-party instance or self-host as an option.

I've seen multiple fediverse project dead before arrival, as the dev working on other job(s) for living. Heck, that's also the same reason why most of fediverse project are from the West, a lot of people who lives in a country with low paygrade (including me) are not able to dedicate their time for FOSS project.