When I worked in a call centre I had to talk all bloody day.

I used to perform vocally a lot growing up though (age 3-19), so my theory from spending so much time on stage, is that some people just have stronger vocal chords than others.

Its why I can sing at the top of my lungs for 3 hours straight without consequence, yet my sister loses her voice when she attempts the same thing, or my brother starts singing softer or in a different key after the 1 hour mark.

Idk, that's just my personal take on it.
I'm no expert on vocal chords.