I think your niche skillset is probably the main reason, I doubt many FAANG people at an engineer level in the UK (especially outside London) make anywhere close to that.

I've been getting offers on that range in London for a few years now but they're senior management roles and I have a pretty unique skillset, FAANG recruiters haven't even bothered contacting me for like 10 years (they were chasing much harder when I was a junior engineer)