Twenty-somethings today don't remember a time before the smartphone era when there was a race for phones to be smaller.

Cell phones were initially huge. Actually, first they existed as "car phones". They were heavy boxes the size of a big bottle of laundry detergent, bearing a handset with a number pad. They operated on AMPS (analog mobile phone service). After that cell phones then became smaller and more portable, but still huge, resembling household cordless phones. There was a race in the 1990's and early 2000's for smaller and smaller phones. Having a smaller phone than the next person was a status symbol.

Smartphones have disrupted that trend, because small touch screens suck. The trend has not entirely been disrupted: smartphones cannot be too large. Then they turn into tablets. And, thin matters, still.