It should be a trend. I've been wearing a crossbody small bag (I guess you could call it a fanny pack, technically) for a long time now and ever since I've gotten a smartwatch I rarely need to take my phone out, so it lives in the bag instead of a bulge in my pants pocket. I wear the bag in the front so when I do need my phone it's just as quick to pull out of the bag as my pants pocket.
I wouldn't be surprised if discomfort from having a bulky phone in your pocket drives this.
I am also guilty of buying a bag (not this kind) for my phone because it's so much more comfortable (and makes my trousers last longer) to not have my phone in my pocket.
This was my first thought. My iPhone 15 Pro is fine and hopefully has much more life left in it, and I've gotten used to the size in general over the years, but I like to wear pants that are reasonably fitted and the "pocket bulge" outline of the phone still annoys me if I'm trying to deliberately look nice.
I'd believe this is an area where even a few millimeters of thickness makes a real difference in how much the phone in pocket stands out despite the overall footprint being larger? Will be curious to read once people get their hands on the things.