Really am sorry for the behavior of community of stackexchange math, I am the first who has marked this question as a duplicate question and I have got some up vote for this comment After sometimes, I have got my comment deleted and the question become marked by others, Why this behavior? Really I decide to leave this website this is not good behavior
I am sorry for the frustration, but it is of nobody's doing, specifically.
The automatic comment posted upon a vote to close as a duplicate or also a flag as duplicate, the current case, gets automatically deleted by the software once the vote takes effect, because it is considered as redundant. As a general principle comments that are no longer essential get removed.
The people listed in banner are those that voted to close as a duplicate, while you had flagged as a duplicate. Soon, once you reached 3000 points, you will be able to cast a vote as a duplicate, too. In this case the comment will still be deleted, yet you then will be listed in the banner.
Indeed, unfortunately, the information that you had flagged as duplicate is now not very visible anymore. It might be that this side-effect was overlooked, due to the fact that flagging for duplicate is a latter addition, and it is less of an issue for voters (but I am not completely sure about this).
In any case, your flag was useful and appreciated.