Had the opposite issue - too narrow a stance 'cause that inside boot/leg was a lazy passenger resting against the outside boot/leg. (Well, that's the way it looked like they were skiing when growing up in the 60s/70s so that's what got copied/imprinted.)
Proved a challenging habit to break. For a couple of years every single instructor commented and tried to address. The independent leg action got resolved some time before the aesthetic - the aesthetic being knock knees made the stance look narrower than it was. Some of the drills were, ah, well meaning but not so effective. Like poles in the form of an X between legs levering them apart - sort of a good way to proceed to the scene of an accident. The one that eventually did the trick was to skis behind another skier and have my skis makes tracks either side of their tracks. 3 to 4 runs of that exaggerated, wide stance and not had an instructor comment on stance width since.
Might be interesting to try the reverse. Have a leader ski with a wide stance and the follower has to keep their tracks inside the leader's tracks.
Do wonder at comments here that a wide stance makes it more difficult to transition or less effective or whatever. Hirscher used whatever stance width (at transition) he wanted/needed (wide, narrow, in between) and seemed to manage just fine. GS or SL. As does Shiffrin, Ligety, LGB and likely a host of others. With the possible exception of The Rocket.
There's likely a broad range of stance widths that are effective and much depends on the context/intent. Not expecting it to get added to CARV's list of metrics.
The primary difference is speed. When traveling at much slower speeds, it's much harder to "get over" (aka topple) with a wider stance.