So you need to look at the number of de federations. That is basically how many other instances have blocked them and do not receive content from them to their feed. You can still go to all these instances using their respective urls and see what they are like. The reasons for blocking them vary depending on the instance. Edit: They can still be federated with other instances that don’t block them creating their own little fediverse bubbles.
The nazi-pedo bubbles.🤮 You’d have to go to their instances to see, a lot of lemmy instances have the blocked list public (sometimes there’s the link at the bottom of the page) Example Example2