Dodging loses you LP because otherwise you can just dodge indefinitely until you get the perfect team comp you're looking for, which ofc, is not only a bad mindset to promote, it also basically kills the game because barely anyone would be actually playing as almost everybody would be stuck in infinite dodges in matchmaking (since everybody has their own personal definition on what a "perfect team" is).
Implementing "legal" dodges from trolls is another matter, though. Because it first comes down to what qualifies as "trolling". Sion Carry and Janna Top are all actually viable play options, and is not to be dismissed at face value just because you BELIEVE it is not viable or because it's not the most optimal. What constitutes as DEFINITIVELY trolling in champion select? You see, it can be hard to pinpoint sometimes, let alone making a system, that can't be abused, that builds on it which allows penalty-free dodges.