We know you lose more than you win by rolling. The question was not "Will you lose more than you win?" The question was "Why are the rules written that way?"Some people like to spend half their paycheck on lottery tickets, too. Doesn't make it a wise choice.
I remember playing a wizard back in 2e who had a whopping 8 hit points at 5th level. Rolling is fun, but it's a gamble. If you want to gamble, you have to accept the risk that you will likely lose more than you will win.