It's not just TheShrike, it's a decision from all the moderators. All to often some newb makes a sig thread, does 4-5 and then lets it drop, or they make a new one when theirs sinks past the first page, or gets locked, and or deleted.
Then we have the people that literally make new ones every week, or more.
It's just a waste of space to have 3-4 sig threads in general, at any time, by different people. This action, is aimed at the people who make a thread, and abandon it as soon as it's older than a couple of hours at the very least.