It prevented it by having a hardware module on the CPU's memory controller that AES encrypts the contents you are sending to DRAM, and decrypts it before reading it back to the CPUs memory structures. All with hardware keys completely invisible to software (and one that is basically impossible to manipulate physically).
And you need to be able to do it multiple times for the bits of memory that you want to snoop on, to be the bits that survive the transfer.
A feature that was possibly accidentally enabled on consumer chips is now being disabled. I would guess that the number of owners of consumer chips who also relied on them for encryption is exceedingly small.
The primary concern persists. The manufacturer has an exceptional amount of control of the state of your CPU most of which you cannot change and an unknown chunk of which you cannot even see. We are sort of playing in a fools paradise.
They either have that control or they don't.
So it's quite possible they were doing the same with TSME, and either made a rude marketing decision that the people using it on consumer chips would probably pay for PRO chips if they were prevented from doing so, or kept getting people attempting to RMA the chips for a feature they never said worked on them not working, or there's some systemic flaw in the consumer chip's implementation that they didn't feel like trying to qualify fixing versus just killing the not-guaranteed support.
Hard to guess without more data than just them going silent about it.
I guarantee you that there's one small company that put 1,000 of these chips in a server room or datacentre though, and they're now completely boned.
Bro what are you smoking? The highly paid and experienced engineers designing these chips could have "possibly enabled" the feature on consumer chips.
The chips were designed with the feature as it is cheaper to do everything right from the get go and disable functionality rather than design a less capable chip then tack on the feature afterwards, just as the consumer versions of Windows are the server versions with functionality removed.