The simple answer is that Limited was already a 140mm mag length limit, so in 2017 when they upped CO from the 10-round limit that it started out as, the easiest thing to do was to adopt Limited's mag length. Now that LO is a thing, I really doubt the division will go away, so I think the best thing would be to keep LO at 140mm, raise Prod to 15 rounds, and lower CO to 15 rounds to help return it to the Production-with-an-optic division that it was originally meant to be.
Carrying mags with extensions isn't uncommon though. I carry a factory Glock 24-round magazine as a reload fairly often, and it's ~155mm.