Startups like Wayve AI most recently raised $1BN in the UK and still pays AI engineers lower than US peers.
Only FAANG and banking can pay high salaries in London.
They complain that they can't find "talent", and my cynical take is that the scheme is to get immigrants on sponsored visas who will do that to get to the UK then move job when they can.
They either need to decide they can't afford to pay decent wages (and therefore go out of business), or decide that they can (and start doing so). As a bonus, if enough of the bottom feeders go out of business, demand for living in London might go down, and housing could become a bit more affordable there.
Or it's a scam to try for cheap immigrants, as you say. If that's the case, they need to be rebuffed by the immigration service.