Very interesting point, I belong to several forums, both car related and not, and I am noticing this is becoming a problem on a couple of them, reduced forum visits etc, but one of the major changes seems to be that the advice on the social media sites is very poor and uneducated.....IE lots of incorrect and bad advice, along with lots of sales also, so unfortunately I fear that it may be ultimate demise of the forum as we know it.
I hope not but its looking that way, some of the problem I think is due to forum owners feeling that also using social media sites is beneficial, but in the long term as you say it an easy fix for most and will I think kill off certain forums.
It will be a sad day if the forums no longer exist. IMHO, they are so much better than social media sites