That is sick. They paid below market rent for 10 years and held the owner hostage, now they deserve a prize for playing (and in a sense winning) that game? הרצחת וגם ירשת? The standards for ועשית הטוב והישר should go both ways and the landlord has certainly held up his part of that.
It's not neccesarily fair, but it sometimes is the easiest/quickest way to make the 'problem' go away, instead of having to go through the courts.
it also allows the issue to be resolved in goodwill rather than recrimination.
If the sale is worhtwhile enough to the landlord, a small 'buyout' may be worthwhile