I blame the splitting of the forums. You're right though, it was crazy. You could post a thread and it would be gone off the first page within a minute if nobody bumped it.
The splitting of the forums is half the problem. The other is the traffic really did go down by a huge amount, much of it from the banning of users (this is really noticeable if you look at old threads, sometimes 1/10th of the posters are banned) and some users just moving on in life where they don't have as much time (like yoyo). There's a much lower influx of new members, too, aside from the occasional spammer. I think in part it's due to the PC hardware as a hobby declining, is traditional desktops versus tablets and hybrid laptops.
A lot of the more technical, mobile minded people are probably still finding the site, but I fear the younger generations (now I sound like an old man, though I'm in my 20s

) tend to want more casual analysis like what you can get from The Verge and Engadget as opposed to the traditional tech sites like AnandTech and Tom's, though even here the main site is adapting a bit.
Hot Deals really, really dried up here, too. From all the "how did you find AnandTech?" threads you can tell many people found ATOT because of Hot Deals. It's how I discovered this site.