I have noticing for the past few months new comers are getting banned the day they signed up.
I need to know the reason of them for getting banned.
It's because they are mostly spambots, registering just to post a thread to advertise for some official or inofficial product or service. They are easily identified by having just one post. As the advertisement threads are removed as soon as a mod takes notice of it, there is no evidence left of it.
tl;dr not really newcomers or humans but spambots