I'd suggest starting with some market research. The clothing industry is said to be pretty responsive to customer demand, with fairly low barriers to entry. Why aren't your future competitors already cashing in on this problem?
There are womens clothes with pockets, also womens cargo pants exist, but in the end, most women buy other stuff, and most non-specialized stores sell stuff that women (..well, and men) buy the most.
Women, believe it or not, are just like men, in that they are human beings.
As human beings, women (just like men!) have a variety of competing preferences that all must be balanced in the presence of a limited budget set.
It's totally possible to find women's pants with big pockets. It's also possible to find women's pants made of high-quality materials. Furthermore, it's possible (if you browse carefully) to find women's pants that have a relatively neutral straight cut, but still fit nicely around the hips, thighs, buttocks, and waist.
What's broadly impossible is to actually find all three of those characteristics in the same pair of pants. If you buy pants at H&M, they might fit how you want, but they are going to fall apart. If you buy pants at Marshall's, they won't look good and they might still fall apart. If you buy pants at Madewell, they are cut assuming the wearer is a scrawny teenager, unless you specifically size up into the "plus" category. Etc etc.
What's also borderline impossible is to find pants that fit in both waist and leg length if your body proportions are not that of a limited prescribed set, because women's pants are not sold according to separate waist and leg sizes. But that's a separate issue. It actually exemplifies the problem here, but that first requires us to think about adult women as adult conscious intelligent human people and not as abstract instinct-driven chimpanzee-like entities. So let's not go there.
The overarching problem as I see it is that there are no women's pants that are just normal pants. There's always something funky about them.
Remember, I'm not just talking about knockaround faded blue jeans. Pants are worn for a variety of reasons. Go to any urban downtown area and look at the men who look like they're on their way to work. Several of them will probably be wearing high-end selvedge denim or twill chinos. The lower leg will be straight and slim, landing more or less at the correct location at the top of the shoe. The thigh and seat will be fitted comfortably but not baggy. The material is sturdy and high-quality. There is no unnecessary wear applied to the pants, no feathering, no tears at the bottom edge, no holes at the knees. The pockets will be standard size, big enough for the wearer's oversize iPhone XQBERT 45 with 6 cameras in one pocket, and their tactical EDC card clip in the other. They will likely also have some kind of shoulder bag or backpack, revealing that they do in fact desire to carry items that don't fit in a standard pocket.
Find me a pair of pants like that in a cut appropriate for a woman's hip/thigh/seat proportions, and I'll pay you a finders fee, because my wife would be very interested in purchasing them.
Damn dude, I didn't ask to catch strays like this :(
https://www.hexagona.com/fr/sacs-bandouliere-sacs-banane/553...
Otherwise, the company(ies) that don't create purses don't make more money selling purses + pants.
Of course, there could be a new company that makers neither pants nor purses that gets into the pants making business.
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It's aesthetics, pockets don't make a woman's figure slimming so they don't sell as well.
I've heard many women complain over the years about the small pockets, but my assumption (possibly very wrong) is that they might not buy a pair of jeans if giving them full sized pockets made them significantly less fashionable (i.e. they'd get less utility out of them).
Talk to those women and they will admit there are many clothes for women with pockets, just that those doesn't look as good so they are searching hard for good looking clothes with pockets which basically doesn't exist. They rather buy clothes they like without pockets than clothes they find ugly with pockets.