I agree that developed companies are doing what is described, but that is a completely separate thing than starting from scratch.
People have hurriedly forgotten why Linux distros exist: https://opensource.com/article/19/2/linux-distributions-stil...
Even when you write a lot of software, environments always drag in existing tools and infrastructure (aka other open source). 99% it's easier to consume pre-built SME knowledge from. Linux distro #HailTheMaintainers