I would also add that everyone is evaluating the tech stack of these companies in today's context. Google was founded in 1998. Facebook was founded in 2004. Ube

I would also add that everyone is evaluating the tech stack of these companies in today's context. Google was founded in 1998. Facebook was founded in 2004. Uber was founded in 2009. Microsoft was founded in 1975. Amazon EC2 was first offered in 2006 and was super new and immature for a number of years. Kubernetes was first released in 2014. Mesos was a research idea for a number of years starting in 2009 and didn't reach version 1 until mid 2016. Etc. Etc. These companies generally invent their own solutions because the solutions everyone here thinks they should be using didn't exist or were not stable at the time they had a problem they needed to solve. By the time those new solutions exist and are stable enough, it requires quite a bit of investment to migrate to the newer solution as these companies already have much of their tech stack stable and bringing in revenue on their in-house solutions.