If their question lacked an attempt or any details, we could just tell them couldn't we? Why not vote down only those questions which either can't be understood or are off topic? Are people trying to scare away newbies or something?
Votes and comments serve different roles.
- I leave a comment when I want to tell something to the author.
- I downvote when I want to signal (not just to the author) that the question is of low quality.
Sometimes it's both, sometimes just one of these.
Votes enable actions that comments don't. For example, one can filter questions based on their score, excluding all downvoted ones. Negative score also reduces the visibility of questions, and facilitates automatic deletion.
Why not vote down only those questions which either can't be understood or are off topic?
Those should be closed and deleted, not just downvoted. By the way, homework dumps are off-topic here.