I don't think OP is right at all. Just because a company offers managed instances of any random FLOSS service that does not mean they are profiting out of that service.

From the customer standpoint, the choice is between running self hosted instances on bare VMs or use managed instances, and if managed instances are not available then they don't have a lot of alternatives. Managed instances are cheaper to run and operate, and are more reliable, thus it's more advantageous to use those services. For the cloud provider, they are getting paid either way.

It's not like function-as-a-service offerings, where cloud providers charge users a premium for computational resources that run on spare cycles and allow far higher utilization rates, thus getting paid in two or three different ways.