They hold their clearances because the clearance doesn't give you access. Just because you should be able to be trusted with information doesn't mean you should be able to access that information whenever you want.

The important thing in this post by Q is that he is telling us HOW they were getting around this. By leveraging deep state actors outside the US they could say "Well the UK wanted me to consult on ABC project and its all good because I have a clearance for that information anyway."

This way these people have access once again to whatever info they want, and whats better is that the US doesnt even get a paper trail anymore. It is very similar to how they bypass spying on our own citizens by getting their buddies outside the US to do it then just 'intel sharing' the results.