Except in the US, and a handful of other countries who do have fixed length numbering plans.
I know in my part of the world we went from 2-digit local numbers to 3-4-5 digits, to 8 or 10 digits over a century.
My point being this is simply routing implementation details. Even USA has 911 for example.
Most of the phone numbers were something like 01 361 1234, i.e. seven digits after the 01 area code. The _361_ part was bold, so I think that was an exchange number.
A few numbers were something like "Placename 12345". Wikipedia explains why that was.