Whether something is funded by donations or fees is separate from whether the cost of people’s time should be included in the revenue target.

Yeah, but where are the admins who dare to say “I think my work is worth $15k/month, so I will only keep the instance open if we collect that much money”?

There aren’t, because the majority of users will see that “profiteering” and flat out refuse to contribute. Or they will come up with the worst excuses to diminish the work of the admins, which in the end translate to “I don’t make that much money, how could I justify accepting that your work is more valuable than mine?” crab mentality.