Recently RedHat was transitioning from selling the VM based RHEL to the cloud native OpenShift. They used the relationship they had with customers already using RHEL to 'up-sell' them to OpenShift.
IBM already had a SaaS offering for Kubernetes in https://www.ibm.com/cloud/container-service and RedHat adds a strong self-managed offering for Kubernetes in the form of OpenShift.
IBMs revenue comes from consulting but a lot of their profit comes from software https://www.quora.com/What-is-the-split-between-IT-and-consu... They are also a trusted advisor and are great at closing large and complex purchases. This move will allow IBM to sell more software products and therefore increase their margins.
I have a lot of respect for RedHats policy to open source all the software they sell. I expect that policy to continue.