I assume this is due to the advent of touchscreen phones. Around when people were getting used to the idea that mobile phones could be used for more than just making calls, touchscreens could be buggy/laggy and there wasn't haptic feedback or any sort of attempt at recreating the physical sensation of typing. RIM doubled down on physical keyboards, and Blackberrys had great ones (I could type much faster on my Blackberry Bold than on an iPhone at the time) and they already had productivity/utility apps and such since they were really PDAs. But the gradually improving touchscreen typing experience, combined with the increased utility of being able to put the keyboard away when you didn't need it, spelled the death of physical keyboard phones not long after.