I suspect price segmentation is a big reason for that. Apple's always been competing against a wide range of prices in the Android space.
SE: only small choice, starts at $349
6S: 449
7: 549
8: 699
6S+: 549
7+: 669
8+: 799
So each "normal" size is available at 3 price points. Horace Dediu has talked a lot about price segmentation and umbrellas in the past; this seems like a perfectly reasonable strategy, and I doubt people are all that confused about what they want. Pick a size, pick a price point, buy.
SE: only small choice, starts at $349
6S: 449 7: 549 8: 699
6S+: 549 7+: 669 8+: 799
So each "normal" size is available at 3 price points. Horace Dediu has talked a lot about price segmentation and umbrellas in the past; this seems like a perfectly reasonable strategy, and I doubt people are all that confused about what they want. Pick a size, pick a price point, buy.