If you don't honor contracts, then you should go out of business, because nobody will trust you (if they're wise, though there are always some people/companies who will be foolish).

If you make a contract that involves you receiving a one-time fee for something that will cost you far more than that fee, then you will eventually go out of business for being stupid.

Yes, there are hosting costs and maintenance costs. So the original deal (pay once for something that costs us ongoing money) was a stupid business decision. Doesn't change the fact that they undertook to make that contract. So now they should be held to it.

And the fact that someone else bought them does not invalidate the contract. When you acquire a business, you acquire their contractual obligations. As it should be, otherwise contracts cannot be trusted in the long run.