Commenting is important:

1. It's easier to comment then writing a post.
2. You can make friends by commenting.
3. If your comment is on point, about the post you can easily get some upvotes.
4. Answering other's questions or replying to comments and helping other can again bring you some upvotes.

Usualy only spam bots comment with 1 to 3 words and they spam all the posts with the same words.