Tbh I dont think that the traffic data Ive seen suggests that there was a long term drop but subjectively the content on a lot of subs has dried up substantially. It seems like people still go there but the actual content being made is just a trickle compared to what it used to be
People that create content are arguably much more likely to have used the apps that were killed off and much more likely to recognize what reddit did as something that will eventually lead to it being irrelevant. The latter reason is why I dont go back there much. I watched Digg and Slashdot become irrelevant has beens and Reddit is on a fast track to join them.