because there are no real alternatives. Everything that could be considered an alternative has drawbacks or things that are missing. Proxmox comes close but doesn't offer proper enterprise support contracts, so you'd be stuck with a 3rd party.

Then there's training. you can't easily switch your admins and service desk techs to a different product. That alone takes months, of not years, and costs a lot. Rewrite all processes, etc.

Then there's 3rd party integration. Since VMware was basically the "default", most 3rd party products offered turnkey integration into VMware, and VMware only. Think backup applications or security etc. You don't switch backup vendors easily (for the same reasons - training, features, ...) and if you do consider it, it adds to the cost

This is why, for many companies that don't have 50-100 people or more in their IT department, it's more expensive to switch away from VMware so they grudgingly pay, while trying to move as much workload away from it as possible.