Made-to-Measure is also becoming increasingly popular. While costly compared to brands like Gap and Uniqlo, often you can get well-fitted made-to-measure garments for similar prices to mid-tier brands. For example, SuitSupply [1] offers made-to-measure dress shirts, trousers, and suits for only slightly more than their off-the-rack offerings, and FITTED Underground [2] offers made-to-measure jeans that are still in the price ballpark of premium selvedge jeans. Usually, these brands also let you customize things like button colors, cuffs, collars, monograms, etc. at little-to-no extra charge.
Even some shoe brands like Beckett Simonon [3] and BLKBRD [4] operate on made-to-order models, reducing inventory, and sometimes allowing customization.
All these options still rely on traditional manufacturing, but just the fact that you can get the fit right allows people to consume less.
[0] https://bonobos.com/guideshop
[1] https://suitsupply.com/en-us/
[2] https://fittedunderground.com/
Plus you have to bear in mind that for many people having to make decisions about style, fit, material, colour, pattern is a burden not a pleasure. People just want a new pair of jeans to replace the ones that got damaged so next time they are in Tesco's or Sainsbury's they just grab one off the rail and throw it in the trolley.
You could knit it on a tube knitting machine capable of adjusting loop count/circumference freely.
But for a T-Shirt you have very fine knitting, so regular knitting machines can at best do newborn-sized T-Shirts.
If anyone happens to know where I could order a dozen shirts knitted to spec based on knit design rules and published-by-them loop-pitch-after-first-wash from cotton, I'd love to hear.
Not seamless, but:
There are a lot of brands that offer t-shirts with "raglan" sleeves where the seam runs from the collar to the bottom of the armpit, instead of along the top of the shoulder.
Or: I personally have a number of the Durable Shirt from Ten Thousand [0], which has 2 seams on the front and back of the shoulder instead of 1 directly on top. This is so you can put a barbell on your shoulders comfortably, but I also like the aesthetic. It also looks like they are currently out of stock on these, but maybe they'll have more in the future.
[0] https://www.tenthousand.cc/products/durable-shirt?variant=39...
https://gothaesthetics.com/wp-content/uploads/2020/12/RAGLAN...
Your model might be viable too though, if we use high quality yarn and knit the clothing in a way that the yarn can be respun and reused for the next piece of clothing.