A Rank "Banned" has been suggested before (by me and other people). That would be the fastest way to know an account is banned already, and doesn't need further attention.
Any particular reason was given for not implementing the suggestion?
No.
Actually I am not in mission to catch copy-paster , but they are so widespread in forum that I automatically find them.
I don't look for them either, but once I'm suspicious I check some posts.
A Banned list is not only useful for people reporting them, but it will cause fear in copy-paster too. When they see that so many user are Permabanned , they will automatically mend their ways.
Most of them are probably not smart enough to make that connection.
Mods can see who's banned, but only if they check the profile. A Rank "banned" would be more efficient for everybody.