Most instances also defederated from lemmygrad (commies) so its not generally politically left either.
Also there is the problem of liability, if a instance hosts stuff that is legal where their server stands, but isn't where yours is, you basically need to do it. (Burggit.moe for example, also LemmyNSFW)
Porn in general is also defederated by many because its problematic to moderate.
And then there are instances that just brigade a lot or make bots on mass that spam. They usually get blocked as well.
Last but not least, if your instance defederated nothing it will be defederated because its seen as unmoderated (wich could potentially result in illegal activities)
exohuman