Most Helpful Girl
Most Helpful Guy
It is to prevent spamming.
by the way, spamming = irrelevant or innappropriate messages sent on a mass scale to many people. For instance, a spammer could be someone that posts advertisements via questions repeatedly on GAG to try and spread their word out. Besides advertisements, there are people that most duplicate questions repeatedly to try and get more opinions.
That gets really annoying when you answered it once and you keep seeing it over and over. It wastes time and is just frustrating when you keep clicking on the same question.
GAG doesn't like it. We don't like it. I don't like it.
So the limit is to stop spammers from repeatedly posting the same thing over and over.1