The object of damages is to make the landlord whole. That means if the owner finds a new tenant (or the court finds that he unreasonably did not mitigate his damages and look for a new tenant), the lease breaker only has to pay damages for the amount of actual loss.

There may be some damages for getting the place ready to rent out again and maybe a month of lost rent when showing and getting a new tenant in there. But owners don’t get a windfall (damages & rent from a new tenant) just because the lease was broken.

Landlord/tenant law is pro tenant, not pro landlord.