That doesn't even make sense. Banana Republic cotton is fine. I have a bunch of their shirts and machine wash cold and hang-dry and zero shrinkage.
Did you put it in the dryer afterwards or something? Like I know that sounds dumb but I'm struggling to imagine what could have possibly caused what you describe.
There's zero "enshittification" of the cotton at a brand like Banana Republic.
Do you find there's a difference in cotton quality with different shirt brands that results in some shrinking more than others?
What I'm relating is 100% the truth, and I did not machine dry them after washing. I could not even believe my eyes when it happened, because I've been a customer of their dress shirts since like a decade ago and always relied on them for a precise fit.
I bought two of them, the ones that shrunk. They are labeled as wrinkle-resistant slim shirts, 98% cotton and 2% spandex.
Don't be mistaken, the quality of their apparel has definitely gone down of late. I went on Reddit and its definitely a thing people have noticed.