There are several articles out there that detail the rise and fall of RIM/Blackberry. The basic idea is that Mike Lazaridis and other executives refused to allow the devices to develop beyond excellent email machines with nice keyboards, and completely missed the boat on the kind of developments that people came to expect of not just smartphones, but cell phones in general. Cameras, music players, larger screens, even good web browsers. They also completely missed the BYOD culture - if a person is buying one device for both personal and company use, they aren't going to buy the corporate-focused one that isn't much fun. They're going to buy the Android or iPhone or something with good app support that also happens to talk to Exchange.
By the time they started grudglingly adding some of these features, it was already angling towards too late. By then iPhone and Android (and Windows Phone) were offering near-desktop-levels of web browsing support, decent cameras, every kind of music and video playing you could want, while the Blackberry devices hadn't really changed all that much.
Meanwhile they were at least making enough money on paper with existing contracts to at least stay afloat, which really just led to more head-in-sanding.