As someone who inevitably gets thrown into the "devops" side and the like:
The vast majority of developers can't integrate code or even resolve a merge conflict (and god help you if someone convinced the team to do rebasing instead...). They just stop working and then whine three weeks later during a standup that progress is halted on their deliverables. And, because of the stupidity of "devops" as a job role, there is an increasing culture that development should not have to worry about this kind of stuff.
So good project management becomes splitting up files to minimize the chance for conflicts and spreading tasks out to minimize the times people will be in the same file, let alone function. And if they do? Then you do whatever the latest buzz word is for "peer programming".