Comments add a lot of value to the questions being asked or even to the answers. For example, comments can point out mistakes in the question or give deep insights about the topics concerned! Is there any provision where reputation from comments increases only after certain number of upvotes are received on a comment (say 10 votes)?
Help center explains a lot about comments, and is a must read.
Comments are temporary "Post-It" notes left on a question or answer. They can be up-voted (but not down-voted) and flagged, but do not generate reputation. There's no revision history, and when they are deleted they're gone for good.
And go through the tour page:
And we're a little bit different from other sites. This site is all about getting answers. It's not a discussion forum. There's no chit-chat.
Comments are ephemeral, and adding a reputation system to comments goes against our values.
Many comments that are not helpful to understanding the question get upvotes because they are funny or clever. If comments contributed to reputation, every comment with upvotes above the threshhold would have to be reviewed to see if it was substantive.