Pockets in women's clothing are frequently absent, shallow or sewn shut. Each of those outcomes has a separate cause, and none of them is accidental.
The function moved to a separate object
Historically, pockets in women's dress were often tied around the waist beneath the skirt and reached through slits, so they were substantial and independent of the garment.
As silhouettes narrowed, that bulk became impossible to conceal, and the contents moved outward into a carried bag.
Once the bag existed as a separate purchased item, the pressure to build capacity into the clothing itself largely disappeared.
A pocket disturbs the line it is set into
Any pocket adds at least two extra layers of fabric, and on a close-fitting garment those layers show as a ridge or a bulge.
Filling the pocket makes it worse, since weight pulls the fabric and distorts the drape the pattern was cut to produce.
Garments designed for a smooth line over the hip therefore treat pockets as a problem to be solved rather than a feature to be added.
Construction cost is charged per operation
Factories price garments by the operations required, and a welt or a set-in pocket involves cutting, marking, pressing and several precise seams.
On a garment produced in volume at a low price, removing that operation is one of the simplest available savings.
The decision is made at the costing stage rather than by the designer, which is why identical styles at different price points differ in exactly this way.
Sewn-shut pockets serve the shop floor
Pockets on tailored garments are often tacked closed with loose thread so the garment hangs cleanly on the rail and during shipping.
The stitching is meant to be removed by the wearer, and on a properly made piece the pocket beneath is fully functional.
False pockets are a different thing entirely: a flap or welt with nothing behind it, added to suggest a detail the garment does not have.
Demand has begun to move the design brief
Utility-influenced styles and workwear references have brought genuine pockets back into womenswear, and their presence is now used as a selling point.
Phones changed the calculation as well, since a pocket must now hold a specific rigid object of a known size rather than small loose items.
Where pockets are treated as a requirement rather than an afterthought, the pattern is drafted around them from the start, which is the only way to get both capacity and a clean line.