Rebuild $infra from large company and provide it as SaaS was a pretty good recipe for a decent software business for a while. It might still be. For example, PagerDuty came out of monitoring systems at Amazon.
I feel like what's pointed out in this comment is so obvious that it shouldn't be needed ... but evidently it is.
Re:Building Uber’s Go Monorepo with Bazel
by malandrew on Thursday May 14, 2020 @05:44PM
(#23185926)
Sadly, it does need to be pointed out, pretty much every single time. Same with the "Why does company X need so many employees?" question, which you can just reply to with this link: https://danluu.com/sounds-easy/
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.