Specifically, I live in the UK and one of the complaints law enforcement has is that US companies can (and do) totally ignore valid court orders because they don't apply in the US (reddit being an arbitrary concrete example).
So, what would be the impact of GCHQ setting up a scheme where you can sell vulnerabilities to them (assuming they do the legwork to make it legal)? Would it violate some kind of trade agreement? I assume at minimum it would harm diplomatic relations given the pressure the big companies would exert on the US to push back.