Here is a page listing block lists, where you can find plenty of "fun" servers: https://github.com/mastodon/mastodon/discussions/18143

They'll include reasons for the block, which you should pay attention to.

https://fba.ryona.agency/ lets you browse instance block lists, sort by most defederated, who defederates the most, etc. There used to be FediBlock which maintained a centralized blocklist, but it doesn't exist anymore (gee, I wonder how something like that would end up eating itself?).

As far as reasoning goes, I think you can grasp how people would try and wield a tool like blocklists. A lot of blocks are merited, while some arent. I've had several blocks put on my instance from servers that I never even interacted with, for reasons that seemingly appear out of thin air.