From a pure engineering reliability perspective, coupling your technology choice to your vendor gives that vendor too much leverage (as we've seen with, for example, VMware).
This isn't about defending the big companies at all. It's about defending the right of hosting providers to compete on hosting a variety of software. In the alternative world of entirely commercial licenses, or entirely BUSL-styled licenses, you would be shackled to the specific vendors that happened to create the technology that you wanted to leverage. This is a scenario where the customer invariably loses.