If it didn't penalize dodging, people would dodge whenever team comps weren't optimal.
You choose to dodge a Sivir top. Other players may not. You may get a higher win rate as a result of that (since Sivir top is likely to lose), thus to balance it you lose LP for choosing to dodge. It would be unfair to those players who eventually choose to play with the Sivir and eventually lose if you didn't lose LP. If you hadn't dodged, she'd have been in your game and not their queue.
Also eventually she may end up on the enemy team. If you always dodge such players, but there's a chance enemies won't, you'll get free wins by default. That inflates your LP above your actual skill level. An LP dodge penalty brings it down to where it should be.
As for time? The enemy team did nothing wrong - heck they had a free win! Yet their time was wasted because you dodged (and refused to give them that win). Hence, you suffer a time penalty to discourage wasting others time.
Yes, the fault isn't yours if there's a legit troll, but that's the idea behind it. Riot can't know who the trolls are immediately, so they need something in place. I don't want 2 hour queue times.