They may want to, but the real world is one in which contracts are honored either to the extent that it's convenient, or that the penalties for not honoring them are worse than the result of doing so. In other words, "breach of contract" is basically a cost of doing business, especially for a corporation. And, if your counterparty doesn't have the resources to sue, you can get away with almost anything.

Contracts are re-negotiated all the time when circumstances change. Just consider this case: Lambda School paid their head of career services some money to be rid of her under the condition that she keep silent because they didn't consider her trustworthy. Now it turns out that every last bad rumour you head about Lambda School is in fact true, so this person feels that she should keep the money because you can't penalize someone for speaking the truth. We are back at the negotiating table because public opinion is justifiably very much against Lambda School.