I guess I can see reasons why some companies may want to be able to produce time-limited drivers:

Maybe they want beta versions to stop working, forcing users to upgrade.

For offline computers, it might be that some companies would see this as a way to enforce contract periods (customers would have to install an update to continue using the product when their contract is renewed).

Of course, disabling driver signature verification is still a way to bypass that, but often times the companies that do things like this probably aren't thinking about that.

There are usecases for signatures without timestamp.

Besides, literally every codesigning blogpost/tutorial/guide/etc I found tells you to use a timestamping server so the guys and girls and Oculus must have skipped the critical parts of whatever they used.

For what it's worth, I think this is a very sane perspective.