When passing or storing data in code you usually have to specify what type of data is it. An int is an integer, so numbers, there's also boolean (true/false) and many others. There's also string which is just characters of any kind (for the most part) which pretty much makes it a catch-all, since numbers can be a string along with letters and special characters.

But to use a number as a number after it's been received as a string it has to be converted to an int, which means extra code, more effort, more failure points etc etc.