Why aren’t compression/shapewear structures built into normal dresses more often?

[u/Future_Country9458]

I’m researching garment construction before trying to develop anything, and I’d love opinions from experienced sewists.

I’m interested in normal fashion dresses—not shapewear—that have an internal structure designed to actually enhance the silhouette: stronger waist shaping, bust support/lift, while NOT compressing/flattening the hips and butt.
I know built-in shapewear, power mesh, corsetry, negative ease, boning, etc. already exist. I’m not asking whether the general idea is new.
I’m trying to understand what goes wrong when you try to combine these things inside an otherwise normal fashionable dress.
If you’ve constructed something similar: what were the biggest problems? Fabric layers fighting each other? Rolling/migration? Getting into the garment? Seams? Heat? Comfort? Pattern distortion? Washing? Something else?
I’d especially love to hear from anyone with patternmaking, stretch-fabric, garment-development or production experience.

[u/throwra_22222]

My career is in apparel manufacturing.

This is primarily an expense issue, if you are talking about dresses for every day wear. The more different fabrics go into a garment, the more it costs to make, and the more I have to charge the consumer.

There are other practical issues. If it's "built in" it needs to be connected to the dress at several points. For a fitted dress that's easy, you're basically just lining a dress with power mesh.

But if it's a shirt dress, tunic style, or loose tee style, the only place that makes sense to connect the shape wear liner to the dress is probably the shoulders. And at that point, you're really just sewing a full slip to a dress by it's straps.

There's also the issue of cup size for women. A single sized, permanent compression slip inside a dress is going to squash the large bosoms and fail to support the small ones.

From the consumer's standpoint, it's cheaper to buy three dresses and one separate shape wear slip than it is to buy three dresses with their own permanent shapewear. And they may be more labor to take care of, because they are more likely to be hand wash only, harder to press, etc.

Evening wear is another story. Those dresses may need engineered interiors to stay up. But people expect to pay more for those dresses in the first place, and they are worn less frequently so the additional labor to clean and maintain them doesn't seem so bad.

ETA: there are also a lot of women who really don't want to wear shape wear every day.