I know it was rhetorical, but I can answer this question. Because EVERYTHING in a big company is a custom engineering solution. They have their own version of every bit of infrastructure, even when there are clear, robust and proven third-party solution. Because you have an entire hierarchy of engineers, across all levels, actively working to preserve their own job, and doing a lot of self-indulgent work because “it’s interesting” or “I can do it better” or… just because it’s another bit of tech they can patent, publish and profit from.