Tech Talk definitely saw a huge decline in users when the announcement of the SRK forums being shut down happened. Obviously that didn’t happen, but the damage had been done and a lot of users jumped ship.
I do agree with the whole “generational” shift, though. SF4 was big and got people back into fighting games with arcade sticks, followed closely by MvC3. SFV definitely didn’t have the same impact, and I see other popular fighting games nowadays being played with standard controller as much, if not more, than with sticks (DBFZ, BBTAG, etc).
Or maybe it’s just the bulk of us shifting our priorities/hobbies/interests due to life in general. I still love building and modding sticks whenever I can, but I clearly don’t play fighters like I used to.