The main idea is whenever a ban is placed it must follows a cogent reason to back it up,
It mustn't, but I agree that it should show the user the exact reason why he/she got banned. That would reduce the number of threads being created for the sole reason of asking why. All the ban message says is that plagiarism or spam are the most common reasons.
i dont plagiarize and if possibly any reason could have lead to the ban then it could have been temporary ban instead of permanent ban
It's been discussed many times in the past, but the fact remains that if users are find plagiarizing, most of them get permanently banned. Some are pardoned after an appeal, but many aren't.
In this my own case, the reason for the ban remains unclear.
You will have to wait for some input from a mod. I have seen that hilariousandco sometimes explains his decisions if he is the one that issued the ban. mprep is also willing to discuss his view of the rules from time to time.