A lot of people are eligible for carrier subsidized upgrades every few years as well. When I did this I could have gotten my SE2 for free from verizon from my plan. I chose to pay like $200 premium to get it with the highest storage sku.

It isn't just verizon either. Here is metropcs offering free iphone 13s for new customers:

https://www.metrobyt-mobile.com/cell-phone/apple-iphone-13

When the iphone 1 came out on AT&T it was initially sold like that and basically no one had it. Everyone still used their free full keyboard phone with unlimited texting (another american only cellphone market concept that prevented whatsapp from ever lifting off the ground here). Once they got it off that deal and had it with multiple carriers that could offer a carrier subsidized phone, then the dam broke and basically everyone had an iphone or an android phone overnight (same carrier subsidized deals available there, usually better).