The bigger the phone, the larger the surface area for the battery that they can put on it. I suspect that's the primary engineering concern driving it, and it just so happens that customers either like, or haven't balked, at large screens.

Wouldn't a smaller screen with a thicker phone last longer? Less screen area to light up.

I'm curious what the tradeoff is on increased energy consumption is with the larger screen / larger battery / thin phone setup.

Yep. A screen's power consumption grows with the surface area of the screen (w * h) whereas a battery's capacity grows with the volume of the battery (w * h * d).

I think the dominant market pressures so far has been practical concerns like phone thickness and battery life so manufacturers - who are all also competing with their past products - are forced to sacrifice screen size options to compete. Now screen size is becoming unwieldy and screens/batteries have steadily improved so we might swing back the other way.

You could double up on gains on a smaller phone by reducing the screen resolution, which reduces the power demand on the chip managing the display, and so on. Back when I had the Nexus 4, at 720p, I never felt it was pixelated or annoying. Then again, I don't watch movies on my phone either.

On the other hand, given an OLED screen, where energy cost only grows proportionally to the number of pixels receiving power, you could slap a big screen on the phone "for watching movies" but have the phone display a smaller screen centered on it (with black bars around) most of the time. I have a feeling this is the direction the industry would go, if battery life truly became a concern.

I would be happy if they added 1mm thickness to my SE and left the rest. That would allow for quite a bit more battery.

The impractical aspect to that idea is that it would mean creating a new accessories variant. Keeping the same physical dimensions as a previous phone means compatible cases are already available from hundreds of accessory makers.

They absolutely do, services are a larger and larger part of Apple's income.

I believe that's a reason why Screen Time is so bad - it's not a feature, it's just marketing's objection killer.

Why would any phone manufacturer beside Apple care about engagement? No other (non Chinese) OEM makes money from services after the phone is sold.

Do the bundled bloatware deals depend on engagement?

Yeah, that's fair.