My vocal teacher once gave me a lesson on how singers are always something special. Yes, we are. Because voice is a living muscle. You can't stretch it beyond it's capabilities, you can't work with it well if it's swollen or scratched. You can sing by muscle memory if you don't hear yourself, but that's also pretty wild concept - on piano you just press E and it plays E. If you're nervous, all your muscles (including throat) are more tense and you will simply sing a bit higher and need to adjust as you go. And just because I can comfortblably sing around 2,5 octaves it doesn't mean I can just jump or repeatedly and strongly hit one note that's precisely where I change from my throat to head resonation.

It's more similar to rules in gymnastics. Popular singers do not adjust to the songs, songs are adjusted for them.