They are simultaneously larger and less powerful than CR123-powered lights, so there is no pragmatic advantage to owning them. (some people might prefer the slightly different shape, but there's no accounting for personal preference.)
The general public is still largely unaware of CR123A cells, so this doesn't seem like the full explanation to me. I also think that non-enthusiasts are unlikely to invest in the li-ion platform, yet I know lots of people who use NiMh AA and AAA cells. A 1xAA light fits nicely into their existing platform.
I've seen 2xCR123A lights for sale in these stores, but never a 1xCR123A, so as far as the general public is concerned, CR123A lights have no size advantage over a 1xAA.
It isn't even reasonable to claim that they are better in emergencies due to availability of AA batteries, because AAA batteries can always be found when AA batteries are available. In fact, AAA flashlights might be better in emergencies because AAs will probably be in higher demand for other devices.
I think that it is reasonable to claim that 1xAA is a better format for scavenged batteries than 1xAAA for the following reasons:
1. AA has 3x the capacity than the AAA, so unless you're more than 3x as likely to find AAA cells than AA you will still come out ahead energy-wise with AA. Similarly, you can go 3x as long before you need to start looking for scavenged cells.
2. AA lights can use any AAA cells you find, but not the other way around
3. AA lights are easier to keep track of (AAA lights are so small that they tend to disappear with alarming ease)
But really, I just happen to prefer 1xAA since it falls in a convenient sweet spot that no other battery format does:
1. large enough to handle easily with gloves (AAA fails, 1xCR123A often fails)
2. small enough for easy pocket carry (3xAAA fails, 2xCR123A often fails, 2xAA often fails)
3. light enough for holding in mouth when necessary (2xCR123A fails, 2xAA fails, 3xAAA fails)
4. commonly available battery (CR123A fails)
5. commonly available rechargeable battery (CR123A fails)
6. battery commonly used by other electronics (CR123A fails)
7. enough capacity to prevent constant worrying about capacity (AAA fails)
8. no worry about matching cells (all multi-cell formats fail)
I understand that not everyone cares about these things, but I did, in fact, assume that there were others who valued 1xAA for similar reasons.
--flatline