Well, if it's correct (according to what we told in an armorer class just after the release of the G42) that Glock was looking to capture the growing part of the market comprised of women buying .380's, then they seemingly hit their intended goal. They told us that for the 3 years prior to the production of the G42, the fastest growing commercial (meaning non-LE) caliber for sales was the .380ACP, and of that growing market demographic, the biggest numbers were women.
The single stack 9mm market was already pretty saturated with decent choices, but reading between the lines, so to speak, Glock supposedly wanted to steal a little of S&W's thunder with the hugely successful Shield, so they next tried their hand at a diminutive single stack 9. Great sales figures (the G43 was the best selling model in 2016, according to someone at Glock), but it doesn't seem to have "dethroned" the Shield for sheer sales and popularity.
Even though I repeatedly reviewed whether I should buy either a G42 or G43 - or both - before I turned in my ID/badge and lost my peace officer exemption to buy off-roster handguns, I just didn't see a personal need or use for either. Granted, that's because I already own half a dozen compact & subcompact 9's, including 3 single stacks. I have yet to even think I ought to have a Shield 9, either (they offer a CA Compliant model, as it slipped in before the micro-stamping law took effect, so I still have time to change my mind).
I'm not so sure if that would've been the case. For the folks who don't mind the recoil of a very small 9mm, probably.
However, the people who don't want anything that's more difficult to shoot than the G42/.380 might still have likely have sold off their G43's to go to the G42.
It's not exactly uncommon to see some folks teeter back and forth between the choice of carrying/shooting a diminutive .380 and an almost-as-diminutive 9mm. Some folks are more a bit more sensitive to differences in felt recoil than others. Happens all the time .
Kind of like the other group who like to argue about whether a 3" single stack 9 or .40 is "better", and a significant number of folks use the felt recoil of the .40 for arriving at their decision.
It takes all kinds, and the market is full of all of them.