but one thing i dont like is they dont delete your account/details. I dont want them keeping info in database
Bitcoin exchanges are not Facebook.
You can't just delete all the information that is linked to your account without messing up the accounting.
And if transactions remain they have to be linked to an account

It's more to do with the requirements by certain laws on keeping records for a certain period of time (usually about 3 years) in case of any illegal activity.