Seems to me like the concealed carry market is a very small percentage of Glock sales. Glock sells mainly to military and police establishments, nearly all of whom prefer large-cap guns, with a minority of sales to civilians. An even smaller minority of sales is to people who carry concealed. Even if a single stack 26 (or similar) were produced, it would only appeal to some of that small minority, making the slice of sales yet tinier.
While I, as a small-handed shooter, would very much like to have a single-stack 26, I doubt it will happen.
There might also be importation issues under GCA '68.