I think there are many factors, besides the easy economy one.
D11 Tracks arent that great....I heard nothing but bad about bailee....Dirt Country is built on a dirt parking lot practically....COCR USED to be one of my favorite tracks ever but once Kilbarger came out with the latest layout about 2 years ago? I havnt been there much....even though its def one of the better D11 tracks.....personally i do like DMC, its a lot of fun... Never heard anything good about Treaty City....Fast Traxx is pretty decent...Sunday Creek is now run rediculously and way to expensive to do any racing or practicing there.... And the rest are just filler tracks.... If Highland Lakes was still around, id go to every event, i went there their last practice before they shut down just to fall in love with a track id never be able to ride again... I love the elevation change there, layout, everything! Grumpy valley, Kenworthy, Honda Hills, Wild Wilderness and Muskingum Valley were all closed before or right when I first swung a leg over a dirt bike.... And from what ive heard those were the best D11 tracks on the circuit... Regaurdless
The Fair series, I feel, is also killing all the true motocross tracks. If you want to ride an indoor track, do it in the indoor season....not in the summer I hate the look of the fair tracks therefore iv never ridden on any of them, only watched all the numerous wad ups and hillbillys that bring their junk and race in jeans and cause wrecks....just my opinion though. I feel like if it was taken out all the true MX tracks would prosper again. Also scheduleing multiple MX races on the same day, all D11 tracks, is hurting turnouts too....
And lastly I hate waiting all doing and for me, losing my edge between motos and winding down relaxing then having to gear up and go at it again.... idk where practice i can get there, spend 4 hrs there maybe 5 and ride ride ride! and sit just long enough to get some food in my system and let my arms loosen up then get right back to it!!!!
As for D11 vs D12....i always prefered D12 even though i lived in columbus and was closer to D11 tracks id always prefer to ride D12....practice saturday, race sunday! thats the smart way to do it! and D12 gave 2 practice sessions the day of the race for each rider....D11 gives one and no practice day before....its BS! Specially how most D11 tracks have no open practices and i dont feel like giving it my all on a track iv never ridden...except for 3 or four laps that morning...
D12...id been to Scenic, Spokes, Mid Ohio, SVR, Crow, Beans (all but Western Reserve, and Dirt World).....and multiple times!!!! D11...iv been to COCR, DMC, Fast Traxx, Dirt Country, and Sunday Creek...(and theres tons more on their list like Lake Bailee, TCMC, Lakewood, Chillitown, AMS that i've never been to) and about once or twice to each except COCR iv been there for many practice days and prolly 4-5 races there since 2007 when i started racing.
If any District should have closed it should have been D11!!! RIP District 12!