Kailh's keycaps have those dimensions .. for some unknown reason. The MBK profile copied those dimensions. Those are keycaps available to buy separately, while mass-produced keyboards with Kailh Choc tend to have keycaps with more normal dimensions.
Note that Kailh's keycap set also has a bit weird sizes: they were made with a uniform ½-unit stagger, so the Caps Lock key is 2u, left Shift 2.5u and so on. The Space bar row's keys also have non-standard sizes.
Some row-staggered keyboards made for these keycaps (such as the
7sKB) have the mods moved a quarter unit to get normal stagger.
MBK profile is available in only 1u, 1.5u and 2u.