Cap on the amount of remaining aps

No, I mean they figured they could keep it 8 bit and not go to 16 because the only reason for 51 levels of unused SP is if you're hacking or leeching.

They figured they could keep it 1 byte because when you code servers, you need to do some extra thinking. It's not like a regular program where you can use int types for things that can be 0 or 1 (yes i have seen people doing it). When programmers make servers they take some time thinking how to make the server act fast and need less space. One of the ways to do this is using the smallest variables possible for a specific target, which in this case was a single byte.