If they do that and the correct information changes without them updating, they're (rightfully) going to get sued by those businesses. By having it editable by anyone, they avoid that, even if it results in the information being wrong more often.

Proper ways to deal with this would involve employing actual human beings for moderation, for filling in / updating the map data, or for providing support and a verification process to businesses trying to correct their data.

All three of these solutions cost more money than the status quo and are things that Google doesn't really do anywhere, so I doubt this is going to get better anytime soon.