It's a free market. Why do clothing companies not produce them then. If there's enough people wanting them, surely a company would manufacture clothes with pockets and grow to be as large as Untuckit
Clothing companies do produce them every now and then, but they systematically don't sell well, as similar clothing without proper pockets looks tighter, slimmer, and gets preferred by the majority of shoppers.
I would caveat: The majority of shoppers who buy clothing regularly and are into fashion. Which it makes sense for fashion companies to prioritize. Practical women who make pockets a priority also don't replace clothes just because they're out of style, take fewer chances on new things, and buy less.
Honestly, the fashion industry is nothing like computer manufacturing. Costs are very low and most firms have ways to scattergun all sorts of combinations at various ends of the market. Which is why it's interesting that people complain about "no pockets" - that's because there is nothing of the sorts in the shops they patronize, which is likely a very small section of a huge market, selected according to some (typically class-related) criteria. If they were willing to step outside the boundaries of their self-imposed class-sanctioned bubble, I bet they'd find plenty of pockets.
Another point: traditional dressing in many cultures put large pockets on female clothes more than on male ones. The transition to pocket-scarcity on fashion clothes is recent, and probably driven by women rejecting traditional roles. Women voted with their wallets once, they can do it again.