What is interesting to me is how much of that can be self-hosted, and how easily. An ops team is expensive, but so is $490/seat-month. Some of the things you mention are really easy to replace — I am thinking Git hosting locally, replacing Slack with Mattermost, Docker with Podman, Buildah & a container repository, Postman with restclient or Jetbrains with emacs — but for several of them there really aren’t good free alternatives.
You are not taking into account that big corps prefer to buy because it is also a way of doing risk management. You can make legally binding agreements with penalty clauses with suppliers. You can't do that with your own employees, which means you have to know how to hire great people and have the opportunity to pay them well, which is non-trivial.
