Why do people not crosspath fully?

Hey, i’ve played the game for a few years now casually, regularly watch some creators like ISAB and SJB etc. but I notice a lot of them a lot of the time don’t unlock full crosspaths and its got me wondering if I’m missing something, like certain crosspaths actually make towers worse in some ways, or something along those lines? For example ISAB on his recent Lych video had his engineer in 0-1-5 for the whole game up until paragon (and some of the others he didnt crosspath at all), or even the spike factory in 1-5-0. I see this for all sorts of creators in all sorts of different runs and it bugs me, am I missing something? Most tier 2 upgrades are less than $1000 and will surely be a worthwhile upgrade, like paying $350 for the engineer to be 0-2-5 and have that extra moab damage is worth more than saving $350 surely? Especially in early game