Other companies saw that IBM effectively lost control over their platform (and thus lost a large revenue stream), and are determined to not make the same mistake.

That's a long running effort, going all the way from lobbying (DMCA and their ilk), to all kinds of hardware root-of-trust, encrypted and signed firmware, OS kernels and drivers etc etc. And yes, today we have the transistor budgets to spend on things like this, which wasn't an option back when the PC architecture was devised.