TotallyEffed said: "Because it’s rare for any American production to have a British cast album after crossing the pond."
I wouldn't be so quick to say that that's the reason why they didn't make a London cast recording of Hairspray. There have been other Broadway shows that have opened in London and got their own recordings. Kinky Boots, Memphis, an Legally Blonde are all shows that come to mind. Granted, Kinky Boots and Legally Blonde were recorded live but that doesn't matter.
Also, keep in mind, when the London production of Beauty and the Beast opened up in London, they brought the cast in studio to do a London cast recording too.
I think that, although theatre is more part of the culture there, it most likely came down to money. This was before doing cast recordings live became a thing. My guess, if they were more commonplace when Hairspray was in the West End, we may have had one made.