Surely if it's the last prop the whole team should be working together, especially if they are a good runner? Generally on Kaka the last prop isn't an issue unless they are a regular with running abilities
Not necessarily. Just because everyone is chasing/looking for the same prop doesn't mean they're working together. You'll have 5 people running after the prop with flares, some people trying to camp the cp or a random health pack, and perhaps some newish people still unaware of where the prop is. Working together would have one or two people camping the cp, one person at each health pack, some people at designated areas in case that prop heads that way, etc., etc. And this can apply to any map, not just Kaka.
So, yeah, working together and doing seperate things are fairly different. And the majority of people want that last kill for themselves and aren't going to want to work as a team.