Why do transcriptions from Arabic contain numbers instead of letters?

Question

When I was looking for some Arabic lyrics I was wondering why there are numbers inbetween letters in some words (eg. "Aw3a Tes2ny" or "7obak"). Is there a reason behind this?

Answer 1

There are some arabic sounds that don't exist in English. We use numbers to express those sounds.

For example: In English, you use two characters together for expressing a specific sound such as "sh". But In arabic, we don't use two characters together. we use numbers instead.

Answer 2

For the most part, the numbers used are the closest visual representation of the vowel or letter that is not inserted into the word.

3 is the letter 'ayn, and in English, the ' character denotes the letter 'ayn. So aw3a = aw'a,

7 is the letter 'ha,' and in English the h letter can be used (although it's not always used). 7obak is hobak.

2 is the hamza, and there is no hamza in English.

This was the route of speaking Arabic using English. After awhile, multi-language keyboards popularized.