My guess: low background steel is demanded more by low-background experiments like neutrino or dark matter detectors. Most of the LHC experiments work in an environment with enough (intentional) radiation to require special radiation hard electronics. The kind of environment is orders of magnitude more radioactive than the ones where the background radiation from steel becomes important.

But please correct me if I'm wrong!

[1]: https://en.wikipedia.org/wiki/Low-background_steel