ULX uses Source's ban command. Source's ban command, thank goodness, doesn't allow a player to connect just to have them get kicked again by a lua script.
I've seen too many minges try to join tens and hundreds of time, often changing the nick name to show their displeasure.
That alone is annoying to players of the server who see the message, but uses very little resources.
To allow a banned player to connect..snapshot synchronize, download forced downloads, just to have them kicked with a noticeable reason (banned - xxx), would take too much server resources.
As for adding the actual time to the reason, I guess I could see it being handy for the first time they are kicked when banned.