Judging from the few who are commenting I would have to say that there isn't much reason to continue.
Not being privy to the mod's discussions on this subject, I can only guess that there were a few MR members who objected to some of the more blatant signatures where authors are showing large thumbnails of their books. Unfortunately it's easier to restrict everyone to small sig's than to ask a few to restrain themselves.
A few other MR members have objected on other threads about anything other than a few simple text lines. Why they don't turn sig's off as you described, I don't know.
I could make my signature smaller, but I don't think that would satisfy some (or at least one in particular).