Goodbye/Leaving threads are to explain why that person is leaving, and to get more people to read the thread (not for attention.) A simple status update saying "Bye guys" in less than 140 characters would be very unspecific and undetailed, and not many people read status updates. More people would read a thread so your friends would see and understand with the details provided in more than 140 characters, and in a leaving/goodbye thread. Every single one of the threads is unique and would not be considered spam, that would be like considering new clan threads as spam. You say there are 2-3 goodbye threads a day/every 24 hours when there are probably almost 100 clan threads made every day which are much less unique, and I dont see you complaining about those.