The only evidence I have, is what my friends who play league and my personal experience is,(im sure a mod/rioter posted something about it awhile ago, but can't claim that as i can't look for it atm)
I dodge when a game in lobby looks unwinnable, i take my lp and time hits. Now these are rare occurences, but I don't feel they're worthy of a 20 lp loss, when i could play the game and lose 20 lp.
Simply put, if the punishment is worse than actually playing the game, you're keeping people who now are less likly to try or even care about the outcome. As it was decided that it was a loss long before the game even began.
It's a light punishment as a game didn't occur, and nobody else is affected(minor time delay). Its similiar to ignoring the accept queue button. You will get punished for it eventually
In turn I'll ask what evidence do you have to support your claim of needing to increase punishments for dodges?