I think Microsoft is now afraid that people (developers that were hired by enterprises) are willing to move to *nix so much so that they will force enterprises to gave up on MS stack.
This way they could lose SQL Server customer and Windows customer at the same time - having SQL Server version for Linux will keep SQL Server customer.
I believe this wouldn't have happened 10 years ago, and moreover, it would have sounded just unbelievable.
This reminds me not only of things that could change very fast. It reminds that even when things go well with your business there's always someone thing that could "disrupt" your market, like a new dimension. And that thing won't be invisible. It will grow nearby and you will see such company and just won't assume that it represents any danger.