I can think of various reasons to not support BB yet.
- Apps are made with J2ME, an older/simpler kind of Java but yet different;
- Devices have bad Processor and low RAM;
- Lot's of screen sizes and mostly of them, horizontal ( http://supportforums.blackberry.com/t5/Java-Development/List-of-Blackberry-Devices-with-resolution/td-p/556066
). The only screen that is the same as iPhone's is BlackBerry Torch 9800, with 320x480. Others are 360xNNN or 320x240 etc.
- NON EXISTENT 'WebView' in OS 5.9 or older. It was only (bad) implemented on 6.0 and with lots of restrictions <== The MAIN factor, together with buggy browser.
These are the facts I think of now with my experience developing for BB.
But I think RIM might start offering better phones with better OS and better browsers since they changed browser rendering engine to WebKit (was a proprietary one prior to 6.0) so we might see something coming someday.
Don't lose your hopes ;D