I think the Blahaj instances are just focused on creating a safe space for trans and other minority users, and downvotes are one of the targeted ways bigots can harass, so it’s just disabled for that reason. That said, trans folks don’t tend to strike me as snowflakes - we get a lot of hate and flak IRL and on the internet so a lot of us are pretty used to it. It’s just nice to have a space where we don’t have to worry about it.