Logic Behind Security Deposits for Apartments

[Collude]

Ok I understand if you wreck the place etc any damges done would be taken from that money. But what I don't get is this.

My apartment replaces all carpet and repaints when someone moves out. So why would they charge me for damages to the rug when they was replacing it anyways.

Now I know it's just because they want to make money from every possible angle. But is their any logic behind this besides them trying to scam people out of money?

If the carpet is being replaced anyways why should the renter have to pay for the carpet that has stains thats getting torned out anyways?

I'm not in this situation I'm just thinking fo the future