You have to weigh these risks against the likelihood of them actually happening. If AWS made a first-ever price increase, yes, you'd then have to consider whether you could beat that pricing by doing it in-house but you have to balance that against the very low odds of it actually happening and the up-front costs of hiring a ton of staff (e.g. just having 24x7 support requires something like 5 people when you factor in leave, vacations, etc.), buying or renting a lot of hardware, developing and getting operational confidence in a complicated software stack, etc.

That's a LOT of money to spend up front on a gamble that something which has never happened before occurs with so little notice that you wouldn't be able migrate away first. It's hard to see anyone but the major players having enough economy of scale to see positive returns on that investment, much less having enough budget room to where that makes sense rather than spending the same amount of money on something which users actually see.

That gets to the other reason why this is so unlikely: raising prices in a predatory manner would be a loud message to every AWS customer to find alternatives. Since AWS generates something like 7-8 billion dollars a year that's an enormous amount of money to risk — far greater than any short-term return they'd see.