@zdarcon Most games don't make it much passed turn ten. So, yeah, that's exactly what we're saying. If it was a common occurrence for games to cross the twenty threshold, maybe... But let's not kid ourselves, twenty turn matches are incredibly rare.
That being said, with less cards giving you a higher likelihood of getting what you need to win, matches would potentially be even shorter.
It's basically the same reasoning behind not allowing more than four of any particular card (which some games also allow... Even some that let you have different deck sizes). It increases your likelihood for getting the cards you need for your combos and kill conditions.