Many people saw this as one more move that Microsoft just had to make. After all, given the ubiquitous nature of Linux, every software company has to adapt to work with it, or else forget about targeting certain parts of the enterprise market.
But the real reason for Microsoft's move has now become apparent. It is trying to target Oracle customers and woo them over.
Thus far, Microsoft could only woo Oracle customers who run their systems on Windows.
Microsoft is now offering free lifetime SQL Server licences to those who migrate from Oracle to its database. Some conditions are attached: "Software Assurance subscription required. Some restrictions may apply. Limited time offer—free training and subsidised deployment services available until June 30 2016."
A little less than a decade ago, Oracle announced its own Linux under the name Unbreakable Linux. This was nothing more than Red Hat's enterprise distribution with the trademarks, the only proprietary bits, removed. Nothing wrong with that, it's kosher under the licence which applies to RHEL.
Microsoft can now hold out the promise to anyone who migrates: in a short time, you will be able to run SQL Server on Linux too. And there is much to be gained in terms of money.
Further, given Oracle's somewhat spotty record on security, even Microsoft can claim to offer better support and quicker patches when problems arise. Strange indeed, but true.