The "secret sauce" is vendor lock-in. A textbook case is the vmware broadcom situation. Vmware was cheap so corporations found little reason to use open source. Broadcom made vmware expensive but now those corporations are finding out that it is a lot of work (aka expensive) to switch infrastructure.

The purpose of open source is exactly to fight against vendor lock-in. There is always a way to convert VMs from VMware to open source formats.