*Microsoft* needed Meego dumped – Nokia was financing all kinds of existing desktop & kernel infrastructure enhancements (gtk-side, gstreamer-side, qt-site) for Meego that could all be reused to attack Windows on the desktop and that were all slowly producing results. That's exactly how Red Hat and Suse made Linux a success server-side (and conversely why Canonical is not dangerous for Microsoft – too little infra work, too much NIHism).
In other words, Nokia was not only a threat for Microsoft's phone business, but also for its core products (Tizen and the EFL? ROTFL)
I've no doubt killing Nokia Linux initiatives was part of getting a better Microsoft deal, and that the choice was easy to do for Elop, once he decided he cared more about Microsoft than Nokia (and that was not a given, Paul Maritz did switch priorities when hired VMWare-side).