Short version: bureaucracy and lack of communication in large companies.
Long version: I work for Medium Company, which was bought by Giant Corp. We are still known by the name Medium Company. Although Giant Corp. has a variety of businesses of different types, they are most well known for producing Super Widgets, which are used by loads of large and small businesses worldwide.
Medium Company has nothing to do with producing Super Widgets, but we do use a couple of them. One broke a while back. Getting it replaced should be a piece of cake, right, since we're part of Giant Corp.? Think again. Medium Company employees repeatedly called and e-mailed Giant Corp. people asking for a new Super Widget, only to be redirected to other people or have the calls and e-mails not returned. This went on for a full year
One day, a sales person for Giant Corp. came to our location selling Super Widgets, completely unaware that we are also part of Giant Corp. In this way, after a year of fruitless struggling, we were finally able to obtain a replacement Super Widget.