"Regulations aren't even needed some buildings are just taking care of this issue on their own. "

Not necessarily.

In some cases the ability to have tenants able to rent out their units will allow the landlord to charge more rent for that unit, because the tenant is able to offset the rent. That is good for the landlord, but not good for the other residents who are bothered by the short term rental activity. As others point out it can also add to an increase in rental costs by creating artificial price pressure since tenants can afford to pay more.