It’s worth noting that there are camera differences between the 7 and 7 plus (extra telephoto lens) and the 8 and 8 plus (different main camera, and IIRC something different with the stabilisation...).Well kind of. The new all screen design of the X was the top of the tech lineup Apple offered. Since that new design, they made it even on the more expensive phones. I think they saw a chance to make the max a slight edge to push people to upgrade. I have a theory that most here won’t support that the max isn’t quite the seller Apple would like. They want to push people towards it because the margins are even higher on that model. If they can give people that normal won’t want a huge phone a reason to get it, that’s perfect for them.
It’s fine to have theories about Apple doing devious game theory type things to upsell us to the Pro Max, but I don’t see any compelling evidence. It’s possible that the Pro Max has a higher margin (whether in absolute or proportional terms) than the Pro, but we don’t know that. For all we know component/manufacturing costs could mean that it’s the other way around, or (more likely) that it’s more or less even.
I think Occam’s Razor is helpful here - the simplest explanation is that with a bigger phone, you can put in bigger and slightly better tech.