My experience was that flip phones remained popular in Japan for 2 reasons: corporations that didn't want to pay for data plans for their employees, and elderly people who were more comfortable with buttons. Never heard anyone here say they have one for the size (although they may very well exist)

Japanese is a lot less cumbersome to type on a numeric keypad than English. (The common input method was that every key had a consonant and the number of times you pressed the key was the vowel. Current touchscreen input methods are very similar, using the position for the consonant and a swipe direction (up/down/left/right/none) for the vowel. Wayyyy better than having 26+ touch targets on your tiny screen for English.)