The best part of the fediverse is that anyone can run their own server. The downside of this is that anyone can easily create hordes of fake accounts, as I will now demonstrate.
Fighting fake accounts is hard and most implementations do not currently have an effective way of filtering out fake accounts. I’m sure that the developers will step in if this becomes a bigger problem. Until then, remember that votes are just a number.
As mentioned: It’s not the silver bullet solution but something that raises the bar for abuse. The reputational score is build up over time on the specific server based on the up- and downvotes you received.
So, yes, this can be abused itself as well - but it requires a lot more effort.