Some people downvote a question or an answer but don't comment on what's wrong with it. This is problematic. Either the downvoter is wrong or the downvoted answer is wrong and there is no way to tell which is true, even in principle, without an argument let alone fix any problems. Would there be a way to require a comment in order to downvote it and would that be desirable?
This has been addressed many times, the bottom line is that the admins feel the current system is the best option and mods of individual sites have no power to change things like this. At best it could be made as a "community best practice" if there is total consensus, but I doubt we'd ever get that.