I think it's more likely because PhDs in AI/Ml are extremely expensive to hire. A PhD in AI generally does more than string together pytorch and tensorflow.
Again, in US? I'm from a Russell Group uni, so are friends. Most I've heard of is 37 from a friend that spent over 3 months applying and did some hard negotiating. Can you give some example companies hiring with this salary in UK? I'd be genuinely interested, as I believe would many friends/colleagues.