Ok let's say you're a UK vendor and you developed and published an adding algorithm for 2+2 that returns the correct result: 4
How does that publicised adding algorithm get corrupted, if the UK government decides they want that 2+2=5?
The answer is that matrix being based in the UK isn't ideal, but since they published the whole protocol, it can't just be made unsafe on request without people noticing. If the math maths it still maths when the government doesn't want it to math.
What could happen is that the UK could force specific servers of the UK based entity to surveil targets etc. But you don't have to use their servers (in fact, their goal is probably that you run your own).
As someone who would be in the position to decide for or against matrix/wire usage in my org, I have to say this kind of pratise didn't particularily strengthen my trust in wire.