They had this thread about it: https://hexbear.net/post/1712067

The decision on lemm.ee was much harder as the average user did express desire to remain federated however the admin team decided that a temporary removal from our allow-list was the best option.

as expressed by users belonging to marginalized groups, comments from .ee users are often lib-shit and in some cases outright hostile. While many on hexbear love dunking on these lost libs the duty to protect marginalized users is much more important.

I think the main issue is that for most of the time we were federated, lemm.ee admins were not getting reports about lemm.ee user activity on Hexbear communities (Lemmy didn't have this feature until 0.19), so if anybody used a lemm.ee account to harass users on Hexbear (and I understand this did happen), there was no way for lemm.ee admins to even find out about it. In general we have a very aggressive zero tolerance policy for bigotry (and that includes transphobia), but if we don't receive reports, then it's hard for us to take any kind of action.