My daughter broke her iPhone7. So she pleaded non stop that she needed to get a newer phone to replace hers that didn't function well any more.
The carriers here in Canada were selling the iPhone XR for about $150 more than buying a replacement iPhone7. The iPhone 8 was only $50 less than the XR.. so I bought her an XR figuring that it might last a bit longer in the iOS upgrade functions.
Now does that make the XR a better selling phone to write home about? NO. I needed a phone for her and it was the best value. Would she have gotten an XR if it wasn't for the old phone breaking and Apple refusing to even take a look at it. NO. Was it that the XR had so many features that it was a must to buy? NOPE. Was it that my wife and daughter refuse to use a far superior Andriod Phone over what Apple sells. Well, I guess that is why she ended up with another iPhone.
I don't really understand the threads about how one model line of a particular phone is hyped up as the best seller as without some of the other data to go along with it is just a sales number without relevance. I have had to spend far too many times sitting in the Apple Store getting my ipad looked at, so I talk with other customers. What I find most interesting is asking them why the bought their current phone, what would get them to upgrade to a different phone, and how they would choose the new one.
The answer most often is, PRICE, when it breaks or stops running properly, and PRICE. People don't go out and buy on features irregardless of cost. Apple loves to put a whopping price on their products to give the false sense that they are worth far more than they are, then gives massive insentives through the carriers to move a particular line of phones. The sales statistics don't say if they they were giving promotonal discounts to sell a phone, just that they moved this number.