if someone flags the question, it should be become a mandatory for them to leave a comment

Question

The downvote is okay, but if someone flags the question it should be mandatory for them to leave a reason in a comment or they Should at least forced to upvote the previous flag comments if the reason is same. So that the question can be edited or the user can learn from his mistakes before asking similar questions in the future.

There are only limited options for the flagging a particular question by StackOverflow but it is difficult for the questioner to understand how the question is unclear and how the question is a dupe, with just a comment, problems like these can be clarified and can be avoided further.

Answer 1

As you are probably not aware, this has been requested numerous of times throughout the history of Stack Exchange. The founders and team have been adamant about voting remaining anonymous.

Requiring a comment to (justify) downvote would do away that anonymity. However, there have been changes made to encourage people to leave a comment when downvoting. It is however not mandatory to do so and will not be made mandatory any time soon.