Shimano used to make higher line square taper cartridge bottom brackets, the UN-7X, and UN-9X series, but since square taper cranks are a couple of generations out of date, they have reduced the product line to the single model.

The same thing happened to the newer Octalink bottom brackets. Shimano once offered 105, Ultegra and Dura Ace level road Octalink bbs but now only makes the 105 version.