Another word for the corruption you speak of is friendship.
The key stakeholders and their vendors are friends. They know each other, they get along, they get the product, and like you said, they've built their clout on the know-how of people and product. To choose another vendor, is to disrupt that friendship, and its ancillary benefits, e.g., a ring of trust and a status quo.
I wrote this comment because I've been on the inside. It doesn't feel like corruption when you're in it. It feels like you're getting work done with people you like, just ignoring silly process and distractions that make you think too hard and feel weird. Seeing things differently requires an outside power to intervene, or for the few key insiders to have an ethic that forces them to question their good time and each other.
Most groups of people, not just businesses, punish ethics in pursuit of collective self-interest. That is indeed corruption but it exists so systemically and so personally that I would first call it human nature.
[1] If you read this far, check out ChuckMcM's view on layoffs at Google: https://news.ycombinator.com/item?id=38384254