Lets take a look at one guy making jeans in the US: http://www.roydenim.com/video (video is a great place to start, you get a sense of what the work looks like). But for $225 a pair, its an indulgence.
Also, there are development costs, etc.
Finally, the manufacturer isn't seeing $200. They only get the wholesale price (if they are lucky), or a percentage after the sale. With factories often needing payment upfront, and the brand not making money until after a sale occurs (if ever), there is a lot of risk that needs to be priced into the product.
The rest is pay for himself. It probably takes 6-10 hours to build a pair of jeans at the level he is doing it at, and that leaves him making a reasonable hourly rate
How a about costs for the salesperson in the US? Rent for the store? Branding and marketing costs may be huge.
I recently looked into hand made automatic watches. The main difference between the major brands and smaller (EU based) unknown brands seems to be marketing. You can't pick up a life style magazine of visit an airport without advertisement for watches. This costs money.
Perhaps these guys in the video run too small of an operation to have the costs spread around and to invest in tech to speed up the process.
1500$ dress, has probably $150-200 in material (bought at/near wholesale prices), I'm sure that the jeans in the above video probably have about $20 in material.
Labor is the killer: Cutting, sewing and finishing one of those dresses is a 20 - 30 hour job. There are other costs too, some ongoing like customer service, shipping, marketing, some one time, like grading patterns so that you can make more than one size of an item, or getting photos taken of it for your store.
There isn't really a lot of "tech" in clothing manufacture. Sewing machines haven't changed much in 50 years, the fact that 50 year old equipment is STILL used for production should tell you something about the industry. It is HARD to automate something that is so nuanced.
The way it happens in an industrial setting is the same way its always been done. Lots of people doing the same job over and over on an assembly line. Yes some things have been automated to some degree but not to the extent they have in other industries.
Edit: Yes I have made jeans for myself before, but never at scale.
Same thing though, basically a luxury product.
operate the machine that makes 5,000 pairs a day
It turns out it's ridiculously difficult to make machines that will reliably deal with small, flexible, sometimes-overlapping, sometimes-folded, identically coloured bits of fabric.
You can automate parts of the garment-making process - embroidery, cutting things from rolls, stuff like that - but sewing the bits together automatically is really difficult for a machine, compared to a human.
If you've got clever solutions for this feel free to advance the technology - I'd really like a robot that can do my laundry :)
Maybe one would need to think about entirely different sewing patterns (that must look the part) and cloth stretching/folding mechanisms for this problem.
It's easy to see why you (with current technology) can't simply "make a robot that does what the human does" here.
So, the technology exists, more or less. Like all new technology, it takes time to roll out.
Take something like the humble T-shirt. The process of making those is way more "automated" than it was even 30 years ago. The reason for this is that the t-shirt hasn't changed THAT much in 30 years, and is now more popular than ever. Due to the material, and the pattern, there is a lot of it that is the exact same step between product variations (size, cut etc) or can be done on the same machine the same way.
However, something as simple as pants, not only change seasonaly (shorts) but they change annualy. It is easier for a car manufacturer to build an automated assembly line for welding a frame, than it is for a manufacturer of clothing to do the same for "this seasons" hot item.
For the sake of argument, if we all agreed to wear bellbottoms for the rest of time as our only pants, and to only make them out of one kind of denim, it would STILL be hard for all the reasons mentioned above, but we would have reason to automate (scale). Even then, your producing the pants in 60 some odd waist/lenght combos for men, never mind women, children, teens.
Having recently gotten one of their hoodies, I can say that the quality is excellent vs what you might buy at target/gap/local retail.
But it isn't the stitching or the fabric that is the reason for me disposing of a hoodie (as an example) its going to be staining, or unavoidable damage (snagged my clothing on something).