I think it's mainly the burden of tracking everything.
If all your code is either written in house or source you've explicitly licenced on some commercial basis then chances are there's no problem borrowing a bit from somewhere and reusing it somewhere else.
But suppose you've got GPL'd code floating around, and then someone builds something based on it that's used perfectly legally in-house, and then someone later borrows some excerpts from the GPL'd code and reuses them in another part of the system, and then someone else later decides the GPL'd library/whatever isn't needed any more and cuts it out. Now you've got code floating around that you think your organisation owns, but really it doesn't.
Of course it's possible to comply with the rules by diligently noting any reuse of GPL'd code, and of course there are somewhat related issues with giving due credit even with permissive licences or code you've licenced commercially. But in reality, things go wrong, particularly on long-lived projects where developers come and go. Having GPL'd stuff integrated into your dev process if you're not an all-GPL house just seems like a lawsuit/PR nightmare waiting to happen if you run into one of the more militant groups, and short of imposing expensive and time-consuming audit processes there's not really much that management can do to mitigate that risk.
If all your code is either written in house or source you've explicitly licenced on some commercial basis then chances are there's no problem borrowing a bit from somewhere and reusing it somewhere else.
"Chances are" isn't much of a legal defense. If you're concerned about the costs of auditing and compliance for copyleft software, why not more so for software under less permissive licenses?
Firstly, if you're paying actual money for something, someone in authority has necessarily approved its use and any necessary review by lawyers should already have taken place (and this does actually happen IME).
Secondly, if you're paying actual money for the source code to a library and it wasn't very obviously provided for another reason, it is extremely likely that what you were getting for your money was the right to reuse that code as part of your own project. That's just how the industry works. It's not a 100% guarantee, of course, and standard disclaimers about consulting a lawyer apply, but even if you didn't do that the practical risk here is very low, while numerous places have got caught out when a developer "borrowed" some GPL'd code and didn't tell anyone.
