The most extreme MTB gearing was set in the 8-9 speed era when bikes had 5:1 or even 6:1 range from the top to bottom gear. Although this was "27 speed" it was really effectively 14 speed with 13 overlaps and cross-chains. 10 speeds were often doubles so they didn't really get any more range.

When we started doing 1x for many good reasons, the range of the 42 tooth cassette alone with no front shifter was 4.2:1 with an xD driver or 3.9 with an HG. We tolerated this by deleting the lowest and the two highest speeds. We missed the lowest gear, which led to 12 speeds, which is where we've been for quite a while now. There are a few 13 speed systems but I don't think anyone is whining for more than 12, like they did loudly at 11