David Proulx, BlackBerry’s Senior Director of BBM Business Development, explained that the release of BBM for iOS and Android was due to the large number of users of those two platforms. While Windows Phone might not have enough users to make BlackBerry interested in releasing BBM for the platform, that could change. Proulx says, "As other platforms emerge, whichever they may be, we will execute on those platforms as well."
BlackBerry's thinking about Windows Phone might be dated. While the platform couldn't get popular apps like Instagram for years, that is changing. Apps like Instagram and WhatsApp are now available in the Windows Phone Store. Windows Phone started to gain traction last year and thanks to the GDR3 update, top shelf models have the same specs as high end Android phones.
If Windows Phone continues to pick up users, it won't be long before BlackBerry changes its mind.
source: TrustedReviews via TechCrunch