My guess is they are feeling the hit from Oracle Linux's business model and wanted the flexibility to compete directly.
Oracle Linux's distribution model is that you can take CentOS, change a couple repositories and make it Oracle Linux. Then if you want support, you can pay for it. With Red Hat, RHEL and CentOS before today were separate products with separate release schedules and separate userbases. This move gives Red Hat the opportunity to act more like Oracle Linux if they choose to.
It' almost certainly designed to take advantage of enterprise customers that are already paying Oracle support dollars in some fashion or other, with the slightly advantageous notion of being able to collapse another support provider.
Oracle Linux's distribution model is that you can take CentOS, change a couple repositories and make it Oracle Linux. Then if you want support, you can pay for it. With Red Hat, RHEL and CentOS before today were separate products with separate release schedules and separate userbases. This move gives Red Hat the opportunity to act more like Oracle Linux if they choose to.