Because CEOs do not think long term. They only think in terms of 3-12 months.
Sure they might save a bunch of money by firing their whole work force and using AI. They will immediately gain a shit ton of profit over the next year simply from the lower expenses.
But then their company services will go to shit, customers will get pissed, their revenues will start to decline but that takes years to show on the books and by then they will probably be at some new company.
Not only that, once they fire their workforce and AI cost 2 million a year instead of 5 million for people, two years later AI companies will increase the costs to 4 million. Then 4 years later it will be 6 million. They can't cancel the contract because then they will have to re-hire and re-train an entire workforce which they already had and probably would only cost them $6 million a year at that point if they had kept them.
Then two years later it will cost them 8 million. So on and so forth
They do not realize that AI costs will increase over time a lot faster than what workers demand since workers don't have as many rights as AI corporations, and they will be held hostage by AI companies once they get suckered in.