>You don't see pants coming in one size with the advice "wear a belt".

Great example. Because people who are shorter than average tend to have to get pants taken up, and people who are vastly taller than average tend to go to specialty stores.

The average height of pants is largely dictated by what the market will permit, requiring people to make adjustments or leave the market. Having a 2d matrix of height and width defined pant sizes is too complex for the market to bother with.

Technology is worse, anything that requires tooling is done the least number of times possible. While small phone enjoyers are disadvantaged, they arent disadvantaged enough to force them out of the market. Larger tooling is easier to make and caters to all other preferences.