OpenStack initially emerged as a platform for running a new generation of “cloud native” applications on premise as an alternative to VMware. A few years later it became apparent that carriers and cloud service providers (CSPs) were pouring a lot of engineering resources into OpenStack because using commercial software at that level of scale is simply cost prohibitively.
These days, OpenStack is being used mainly by developers and engineers as a platform for creating new applications. It still takes a fair amount of expertise to stand up an OpenStack cloud. As a result, there is still quite a bit of VMware software running on premise in the enterprise because from a management perspective the VMware environment is significantly more mature.