There exists other reasons to not allow third-party benchmarking, other than trying to hide something. A common reason is as a way to make sure the benchmark is done in a proper way.

I've had the experience myself, and I can imagine that when a system is complex and hard to measure that you don't want an internet journalist running Cinebench to become the reference benchmark for your customers.

Yeah, but what if the microcode killed cinebench performance? Wouldn't that be interesting?

The problem is still the context in which cinebench would be ran. There are so many variable on a complex system that "the microcode killed cinebench perf" could very well be an over simplification of "the microcode in conjunction with this particular motherboard and this version of the kernel plus this particular Nvidia driver lead to a bad interaction that affects cinebench performance negatively".

That's a fair point, though the best solution would be for Intel to commission independent or independently-audited benchmark tests.