Motorola has been one of most notable and adamant backers of the Android OS, the original Motorola Droid and its campaign launched the platform into the place it is now. It not only helped Google and Android but put Motorola back in the driver's seat as their last major success was the RAZR. So Motorola is proclaiming that they are going all in on Android and feel Windows Phone 7 just doesn't offer the features needed to compete with Android.
Motorola's corporate vice president of software and services product management Christy Wyatt said, "We would like an opportunity to create unique value and we don't feel we could with a closed platform."
That is one of the conundrums Windows Phone 7 is in. In one sense they are keeping a tight rein on their OS in a more Apple-like approach, and avoiding issues of fragmentation that Android has been famously attacked for. On the other hand, their offering don't allow for manufacturers like Motorola to customize and differentiate their products.
Motorola mentioned, "There were a bunch of things that we believed about Microsoft that ended up not being true, mostly about what functionality it would have in what period of time." Motorola clearly was willing to adopt the platform if they felt it was a viable option and offered a competitive advantage. At this point it's just playing catch up and Motorola is sticking with what's working in Android.
Source: PC World