No one in management wants the expense or the overhead of actual security. They want the "theater" of security, the good feeling, the box to check on their resume (as management) so everyone can pretend everything is fine and go back to the business at hand. Then something real happens, a leak of user data, or credit cards or internal memos... suddenly everyones job is security and no one knows what to do. The last problem gets solved, there is more "theater" and a few quickly forgotten changes that get worked around or just ignored in the long run.
Furthermore your average engineer wouldn't eat a ham sandwich handed to them on the street by a stranger but will happily run code from 100's of other people on their servers with out even looking at it. Note: I too am guilty as charged. Sure you can vendor it, and miss out on future security patches (it was already broken). Or you could just pull it from whatever repo you got it from to begin with and pick up new flaws. Never mind the fact that pulling from random places assumes that all those other chains of trust remain un-compromised.
Management and Engineers should be the ones most concerend and most thoughtful regarding security and both seem to ignore it for cost and convenience reasons till it is (far too late and) a REAL problem.