There would be no other incentive for companies to buy it.
A company might want to extend it's service offering with a build pipeline/CICD system, and buying GitLab would get them the best-in-class service.
Microsoft bought GitHub for much of the same reasons, and GitHub didn't went to hell after the acquisition.
So many errors in what you've written aren't with the fact that one can INSTALL a copy of gitlab and get the CI/CD features, but actually with simple English.
A company might want to extend it's service offering with a build pipeline/CICD system, and buying GitLab would get them the best-in-class service.
Microsoft bought GitHub for much of the same reasons, and GitHub didn't went to hell after the acquisition.
So many errors in what you've written aren't with the fact that one can INSTALL a copy of gitlab and get the CI/CD features, but actually with simple English.