Also it's needed to remember that Twitter had 100 million users in 2012. A lot of "off the shelf" infra that we can use today just did not exist in 2012. They had to build for scale at that time, and a lot of those choices might not translate easily to something off the shelf now.
First version of Docker was released in 2013 and was a curiosity for a few years.
Kubernetes was launched in 2014, and similarly, was mostly a curiosity for a few years. Twitter at that time made an (probably?) unlucky bet on Mesos, a competing but not that similar technology, that is now pretty much dead.
Google Cloud launched it's VM service in beta in 2012. A lot of base AWS services did exist, but was similarly a curiosity: AWS 2012 revenue was 2 billion. This year they are on track to 80 billion.
I mean, even like J̶e̶n̶k̶i̶n̶s̶ and Kafka were barely a year old in 2012. Hadoop wouldn’t be replaced by Spark for 2 more years. Mesos was in its infancy.
Other companies had similar problems to solve, and they also had to build it themselves for the most part.
