Primarily because of Bibliogram's current state where it almost always just returns a 502 or 503 error on a user's feed. The server that I'm using to host these kinds of services is tightly constrained and I'd rather host something that actually works than hosting services that are mostly broken for an extended period of time. I hope you can understand that. I didn't mean to be rude and I will reconsider hosting it again once these problems are fixed but for now, I stopped hosting it and I thought it was only fair to at least inform you, so that other users are not mislead by seeing my currently discontinued instance in your list. I wish you the best of success, with your project going forward!
No worries, thanks for the info. If you're interested in hosting it again in the future I'd suggest checking again in a month or so whether it works.