Blackberry were living in a dream world. Their targeted market where business and corporate users who paid extra for the premium Blackberry services. It got to the stage where users were paying for things that users on other devices were able to access for free. Mobile email for example. This was one area that blackberry were strong in. The advance of iOS and Android killed this by offering exactly the same thing but built into the OS. 'it was no longer unique to BB, It was no longer a value-added service.
In my opinion, it never was, most phones were already able to send and receive email, it just required a bit of knowledge. Had BB advanced their tech further they may have been able to keep the giants at bay.