It might be time to look at adjustable clothing styles again, but it would require a fashion change as there isn't much that can be done to a t-shirt to make it "adjustable".
Formal/business attire: tailoring is nice but a military tuck lets a dress shirt conform to the belly you have, not the one (or several) it was patterned on.
Casual, work and streetwear: additional snaps, buttons, and ties are often used to allow the wearer to fit to their body and desired motion. Some brands have a show clear intention, such as having a small pleat or even slit in the pant waist with elastic so that it can be worn high or low at a range of sizes. More commonly, elastic pulls on jackets or athletic pants. Others have give less direction but more options by leaving button holes or grommets so the wearer can create their own shape and hold it.
On the consumer end it is difficult to tell when a garment is designed with any of this in mind or if it's just mindless copying or following trends. Having some minuscule knowledge into the design side I can say that it's a mix of both. Brands which care about it have designers who care and try to research these things to use them strategically; they tend to signal the versatility by readily showing models wearing them in different, sometimes unintended ways. Streetwear is ripe with this because brands often produce less meaning less sizes available and they (and their customers) value the suggested creativity. If you can only make S, M, L or M, L, XL but want 5ft women and 6.5ft men to enjoy them that is a challenge which some designers live for.
You just won't find them in Primark for £6.
You could never get good quality clothes for less than an hour of working class wages, it doesn't make sense because they take more than an hour's labour to produce.