It doesn’t really make sense especially since other apps like mail just say idk 9999+ at some point (maybe higher or lower, I’m no maniac letting it get there)

Some developers get lazy and just use an int for everything it's not really a big deal anyway

Ask that question to Java

It's always better to use signed for absolutely everything unless you're dealing with a very edge case

Because it is all written in a language that only has signed numbers. That's virtually all modern languages.