yeah i dont really get why social media replaces forums and chats. These things are so much more small scaled and less all encompassing.
Ever hear the phrase 'get them while they're young' ....
The research I did indicated it had to do with marketing and what was mainstream, along with kids being introduced to social networking on mobile devices (their own or their mothers, as mothers will often let their kids play with their cell phones to placate them) before getting into PC gaming (or anything PC related for that matter). Forums tend to provide a social function as well as a hub of information and/or resources. That social function is what tends to retain users beyond the initial need for info or resources and social networking supplants that in a much easier to interface with format that requires less though. Additionally since many of the things that most people do on a PC can be done on a smart phone by extension the prevalence of home PC's would decline (and it has). The net result is less new PC users and more of those using more casual means of socializing digitally.
Edit: Among other info I analyzed data from gallop polls (homes with home PC's vs. average age data of cell phone users), publicly released market studies (focusing on user account counts, PC related sales, and hand collected re-inforcing data pertaining to new accounts on many forums like this one, GU's, neo-win, etc.) Normally speaking I don't discuss work I have done for clients publicly, but this guy never paid the second half of his bill even though he utilized the data, still uses the website I made for him as part of the contract, and his business was and is doing great. Sure I could sue, but the legal fees would cost me more than what he owes me and that really isn't my style anyway.