I don't really know anything about the internal goings-on around Wizards of the Coast's and Hasbro's push to do away with the Open Gaming Licence as it currently exists, and I don't know enough about contract law to know if they have a leg to stand on. However, I am in no way surprised that they're having a go.
A couple of things have to be borne in mind when something like this occurs.
- First, capitalists are, as a general rule, selfish and greedy, and they don't care about you at all. The only thing about you that is important to them is the amount of your money you're prepared to give them. In most cases, the amount of money that goes into the pockets of a CEO and the other senior officials of a company is directly proportional to the money they get out of you, and capitalists being the way they are, they will prioritize their own wallets over the desires and best interests of their customers.
- Second, in a public company (i.e. one that has issued shares and has shareholders) the management of that company has a legal requirement to maximise returns to their shareholders, and the shareholders can sue if they feel that those requirements are not being adequately addressed.
I don't think that the fact that there is nothing unusual or unexpected about this behaviour means that people shouldn't express their outrage at it, but I have little sympathy with those who feel that they've been betrayed by their kindly roleplaying game production company.
I do think that expressions of hurt and outrage are unlikely to be enough to effect any change in WotC's intentions, because capitalists don't care about your hurt feelings. The only thing that will do that is an impact on their bottom line, and that means cancelling subscriptions and refusing to buy their products until they make a firm commitment to keep the current status quo, vis-a-vis the OGL.
There's a (slim) possibility that this might occur, if the public response has sufficient effect on the company's income. However, even if it does in the short term, always remember that a standard corporate tactic in cases like this is to appear to withdraw, wait for the kerfuffle to die down and for people to become complacent again, and then try it all again. Be vigilant.
Update: 2023-02-05
It would appear that WotC have surrendered entirely (for now) on their plans to gut the OGL 1.0a, and they've said that they're leaving it in place, unchanged. They've also said that the 5e SRD is going to be covered by a Creative Commons licence.
All this sounds very nice, but I'm sure that it will last only until they get some other bright spark MBA graduate on the board who thinks they can squeeze their fanbase without consequence. Memories are short.