I expect “020” isn’t currently a valid prefix in Japan. If so, this makes it a lot easier for software to know whether it has to wait for more digits in a phone number.
There probably are lots of other unused three-digit prefixes, but one has to assume what one deploys now will stay around forever (one century and counting), and that the future will demand space for things we have no idea of.
And 14 isn’t that bad. Bank accounts in Gibraltar (population 35,000 or so) have 23 characters, Kuwait’s (population 4,5 million) have 30, Malta’s (population about 500,000) 31 (https://en.m.wikipedia.org/wiki/International_Bank_Account_N...)
> For “internet of things” devices, 11-digit numbers starting with “020” have been used since January 2017.