The larger issue is that they spilled over into the consumer market in a big way in 2006. When they started to lose market share in the consumer segment in 2012 instead of reinforcing their base in the enterprise market, they doubled down on the consumer market and ended up losing on both fronts. If RIM had turned their attention primarily to their enterprise business, they would in all likelihood still be very successful there and maintained more market share on the consumer side from bleed over in their enterprise customers. Pretty much every tech analyst that looked at the situation said this five years ago, mostly because BB's consumer offerings had very obviously being failing to keep pace with their competition for ~4 years (And were producing some pretty terrible word of mouth as a result) at that point, erstwhile their competitions Enterprise efforts were still terrible.

tl;dr - they got Greedy. Instead of focusing on the fundamentals of their success when competition ramped up, they attempted to keep growing a market they were losing in leaps and bounds.