What are the reasons behind the failure of BlackBerry in the smartphone market?

Main reason is the appearance of Whatsapp where no special code needed or permissions to have chating service with others   

you only need you phone number as an identifier so no need for Bb codes any more 

other smart phone companies adapted many chating services to there platforms such as whatsapp where BB failed  

there are money other reasons too such as 

-the delay to introduce full touch screen devices

-insisting in using there own OS (complicated and not user friendly for some users) and not changing to android