In the early days the number 1 was reserved for long distance calls and 0 was reserved for the telephone operator. And so these two numbers could not be at the start of your number.
So whenever they distributed the numbers or planned on in-scripting letters on the phone, number 1 and 0 were out of question.
The Most Logical
This looks the be one of the most logical reason for this question. On various platforms on the Internet, people have used this reasoning to answer the above question.