What's the point in this exactly?

the point is to gain Total time logged in. even there are not but must be opened bitcointalk

Oh, to cheat the measures put into place to make people earn their levels. I see. Why not just buy an account?

People really are selling their accounts? How much is it worth? It is not bannable offense?

Nope, it's allowed, though some mods/people might frown upon it. Snr accounts tend to go for around 0.4-0.6BTC from what I gather.

Why would anyone buy an account for 0.4BTC as he/she can make a free one ?

Because you could make it back in a week or so on signature deals. Hero accounts probably go for over a bitcoin. They're very valuable.

And now, they can get higher loans from the no-collateral loaners.