Because everyone else in the other threads, for the most part, know better. :B I mean I don't mind a number and then one word, or a picture. BUt when it's just a number I just shake my head.
And saying less than four words usually doesn't make sense in other threads, like Ban The User Above You, Rate/Caption the Avatar/Signature/Song Above You, The One Above, Ask A Stupid Question, and other threads. The only threads where I could see a need for the 4/25 rule coming back would be TCTI and DLTMS0, but people almost always talk in those threads.