BB made a mistake with their BB10 strategy and are paying the price.
Mobile devices are representative of the typical corporate hierarchy - premium 'lifestyle' devices for the execs and basic functional handsets for the general workforce. BB should have come to market with a range of handsets. The drip feed of the Z10, followed by Q10 followed by Q5 meant that only now are corporates considering the move, only the industry is telling them that BB is dying, so they'll hold off on any upgrades. Nokia played the strategy perfectly - 520 - 720 for the general workforce, 820 and above for the bigknobs.
A lot of mid sized companies probably threw out BES in favour of BES Express a couple of years ago. We certainly did. Seeing as BES10 is now commercially licensed again and Activesynch works perfectly well, there's no compelling case for BES10, so no real differentiator betwen BB and other vendors.
Companies really serious about enforcing multi level security have already looked at containerization and are probably well into a PoC of Good or other solution.
It'll never be a 2 horse race and Android and iOS will never be unseated as the main players, but there's a potentially huge market for the 3rd player and currently that's looking likely to be Nokia/WP8