This problem is typically due to one of two reasons:
1) Your video might be set to "made for kids," which doesn't allow comments or engagement on your video (to keep it safe for kids to view).
The solution for this: Edit your video in your YouTube channel, and make sure your video is set to be “not made for kids.” Doing this will re-enable comments to be made on your video.
2) Your video might be an audio upload directly from your distributor (either under your YouTube official artist channel or labeled as "Artist Name - Topic" as the YouTube channel name). In this case, people will not be able to comment on your video. Unfortunately, there is nothing that can be changed to enable comments on these types of videos. We recommend artists promote videos that they upload to their own channel (whether music videos, lyric videos, visualizers, or official audio releases) to have full control over enabling comments, as this helps with the effectiveness of promotion.