@jplyle I think some of the instances have managed to scale, as for making money there are donation systems that some use to help pay the bills.
Third option is for people to run their own instance.
Hope this helps, HOWEVER I am sure others may have better answers.
@zleap all large successful social networks have teams of people working purely on fighting spam and ensuring security.
That requires paying those people very good salaries and I fear donations won’t come close to covering those costs. But I’m sure some smart people have considered options here and I’d love to learn more.