The parties work things out in most cases as reasonable business people can do. The landlord really does want the property back and put to productive use. The tenant really does recognize that the landlord has had to address issues that the landlord had thought were resolved for the term of the lease, and does, or ought to, acknowledge that the tenant should pay a price for this. In fact, there are plenty of reasons why it shouldn't. But the law is broke for the breaching tenant who is treated so differently from the breaching purchaser.
Economic waste is greater.
Landlords have the opportunity to let property sit idle if they are not required to mitigation. Pat says, essentially, that they will mitigate most of the time. Great, but I can just as easily use that point to argue for the requirement as against it. Pat's point and my response include some empirical assertions about how serious the problem actually is. The are crucial to the ultimate choice of law.