This question already has an answer here:
On main sites downvotes are usually used to show that answer is incorrect.
On meta sites downvotes are used to express agreement or disagreement.
On main sites downvotes cost reputation so that people downvote only posts that really worth it as it may give bad feelings to answerer.
But it can't be a reason on Meta as it's explicitly said that votes mean another thing here.
So why downvotes cost reputation on Meta?