It's the new generation. Look at my join date and post count. I've lurked SF and SM for years as I've owned my Supra for about 3 and 1/2 years now but searching the forums had provided me all the information I've ever needed. As the generations get younger and younger and these cars are cheaper, more young people are getting into these cars. I for one prefer forums for the long informative threads but majority of people in my age group prefer social media. I see more "build threads" (more like just pics of updates) on FB/instagram as it's more convenient post on from their phones than it is to post on forums. I lurk forums while I'm at work on a computer, can't really remember the last time I opened my laptop or computer at home to "surf the internet," only when I'm in the middle of doing something on my car and I get stuck so I'll fire it up to search for some answers as it's a PIA or search on phones.
Most of my friends and probably majority of our generation is more into drifting than previous generations (atleast people who aren't afraid to drive their cars) and a lot of kids just buy dollar store rims and Ebay intakes and go to car meets. I've noticed the hate on SF and SM towards stupid suspension set ups and wheels that don't fit without camber, hence I don't care to make a build thread as majority of you will think it's stupid having 17x9.5+12 rims with 245/40 (which is considered a "meaty" set up compared to my IS300 which has 18x9.5 with 215/35 on the fronts) with 2* of negative camber all around, and the people who will like it probably aren't on forums anyway. The older generation is more the "do a proper build" type (which I agree with as well) and probably like drag racing and autox more that scraping side skirts on the floor while sliding sideways. I chose a MKIII to be different, although I have seen a couple driving around, no one I know personally has one in my area and have yet to see one at a local event. Nissan 240's are the Honda Civics of drifting so our generation is leaning more towards them as they are cheaper and parts cost next to nothing with huge ongoing aftermarket support, key word being ongoing. My friends source parts so easily for their cars while I have to turn the internet upside down to find parts for a 1JZ MKIII and am limited to a few stores or go custom. I'm not saying there isn't any support, just not the variety other chassis have, I have a choice of like 2 different $1000 exhaust manifolds for the 1JZ while you can find 10 different SR20 manifolds for like $500. Kids just don't want to spend the money the older crowd did on their cars as they spend more money on partying/eating out/chasing girls and don't want to spend the time uploading pics to a forum. The ones I know who have build threads on forums all are on 240sx forums.
Another person mentioned that the older people are getting into R35's and such, same holds true for any generation. I've noticed my friends who all started with 240's in their late teens now have moved onto more "expensive" cars such as IS300/FRS/BRZ/STI in their mid 20's. Also, I think the discontinuation of the Supra as apposed to Nissan continuing the Skyline has to do with the lack of interest in the Supra as the Skyline fan boys still have something to look forward to as they jump from older generations of the vehicle to the newer generations. MKIII Supra owners jump to MKIV when they can afford it but nothing to look forward to afterwards, the few that stay are the true MKIII fans, such as true Skyline R32 fans. R34 Skylines are starting to get imported to Canada now due to them being old enough (not sure of US import laws) and it's keeping their hype alive as it's something "new", atleast to North America it is. MKIII and MKIV Supras are old news now, nothing to look forward to unless you want to dish out half a million for an LFA. There's very little association today between "Toyota" and "sports cars." I love Toyota to death, but after walking into a Lexus dealership and to have them saying no new Lexus will be manufactured with a manual transmission (other than the IS250) is a big disappointment and other companies again kicking their ass in this category of "fun cars." The FRS is bringing a little bit of attention back to Toyota, but it's also new so dishing out $25K for a new car and the "not fully grown" aftermarket support limits the crowd as well and the relationship between the name "Toyota" and "sports cars" remains non-existent so people are forgetting Supras.