Well, Linux is open source, meaning that the code is publicly available to people to review. That's how this exploit was found before hackers began using it. Windows code is closed source. No one can review it, so exploits are found only by people that reverse engineer the code, without the permission of the publisher. When exploits are found in Windows code, those that find them have only liability to the publisher when they publish them, because they violated the copyright of the publisher when they reverse engineered it. People have different motivation to look for exploits in Windows code than Linux code because of that, and such exploits in closed source code are sold to hackers rather than revealed to the public.

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