As far as the mini phones - because physics - the battery life is atrocious. That was one of the main drivers for me to get a larger phone. Well that and because I can pull down the Control Center and use the widget to make everything on my phone larger and still be able to use it without wearing my glasses. With my glasses, I keep everything the smallest size
The other manufacturers are forced to go along with the market leaders, but sometimes also side-load apps for post-device-sale revenue.
Globally, Apple has what 20% market share? And besides Qualcomm chips, Apple has a complete separate parts supply chain than Android.
Besides, Samsung could definitely create its own small phone and would if there were a market.
Samsung, from what I remember used to side-load tons of apps (some alongside identical stock Android apps), so it's in their best interest to maximise screen time through media apps, which generally work best on a bigger screen.
It's against all of these companies interests to sell you a phone which you quickly use and put away. They all have every incentive to keep you staring, because they're all getting extra money from every ad you see in a game, TV show, movie, web browsing, or wherever else they can slot it.