I mean... it kinda is. Not only is textile design difficult in and of itself (my mom is a very very good hobbyist seamstress, and it takes a lot of work to make even simple garments that work well and feel good), but getting the supply chain running is very difficult and beyond both the skill and patience of most people. You have to be comfortable with not only sewing, but also factory machinery. My mother wanted to make clothes at one point in her life but decided she couldn't scale because she was not comfortable with the large textile die cutting machines that she would have to use to scale.

I dunno who Wyatt Koch is, but if he has designed a shirt and managed to produce it in such volume and with such materials as to be attractive to men (I assume) with money who want to be comfortable, he should be commended. That is very difficult.