I too love my boiled wool Dachstein mittens, alone or in really cold weather under a shell.
I’ve been using a pair for decades (since the 1970s), only had to repair a small worn spot due to my X-C ski poles, on one side only near my thumb (not sure why the hole developed on just one side, something asymmetric in how I hold them or push the poles?).
For warmer weather I too use light gloves, I was thinking more about colder weather.
I think Matt may have hit the nail on the head…mittens are relatively simple to make and the markup is probably less. And there’s not much “fashion” when it comes to mittens, certainly compared to gloves, where there are all kinds of cosmetic and functional features to play with and distinguish your product.