And don't forget _overdimensioning_. Vendors love this because volume scales cubically with increase in any one of width, height and depth -- they're not the ones carrying the phone, but they can pack more features into one, quite literally. FOSS vendors more so since they need more ground to compete on (hardware being older and price being high enough because of economy of scale).

FOSS mobile hardware vendors already have a hard enough niche to target, "people who say they want small phones" is just fuel to the already burning fire for them. Each niche they add does not add the user base together, it multiplies the userbase percentages.

Standard-size phone screens are easier to procure. This determines the dimensions. Same for batteries.