Probably due to the scale they're operating at. Maybe there were parts of things that didn't have such a vulnerability alone but did when put together. Maybe th

Probably due to the scale they're operating at. Maybe there were parts of things that didn't have such a vulnerability alone but did when put together. Maybe there isn't a clear owner of the code so no one felt responsible to find and patch such a thing. Maybe the entire system is too complex for one or even a small team of developers to grok so things can easily slip through the cracks from time to time.