Ergonomics matter too. At this point going thinner is purely a marketing exercise rather than a practical improvement of any kind. If they were able to businesses would be making them so thin you can't hold them without risking a paper-cut so long as that allowed them to convince people that meant it was better than their current, designed for human hands, smartphone. Same thing with size. Personally I prefer a larger display and am willing to accept slightly worse ergonomics for it but even with more or less average sized hands I definitely find phones with 6 inch or under screens much more comfortable in the hand than the more typical sizes today and I know plenty of people with smaller than average hands (ie, half of the population) who really hate holding modern gigantic phones (and so often have held off on upgrading to a new model until I've steered them to something the same size as their old one.)