I blame lack of innovation, or potentionally lack of possible innovation.
The game formula for RTS, especially if you want the game to be balanced, isn't really that flexible. And after a couple years of playing CnC, Dune, SC, Supreme Commander, etc., RTS genre fans pretty much seen it all. And I can't name any rts game from the top of my head that really tried to mix things up. R.U.S.E. comes the closest with the addition of ruses you could use to manipulate the battlefield, but that was really a barebones mechanic. Lack of gameplay variety is likewise a glaring issues. Aside from scripted campaigns, more or less every single match is about destroy the other guy. Sure, there's nuances on how you can go on about it, but it's essentionally just death match.
I'm also a bit biased on that account though, because EA kind-of ruined the CnC franchise and then flat-out axed it for no good reason (the new Generals was looking great and was, despite rough around the edges, very much a game the community liked, until EA simply canned it stating "it's not the game you guys want" (which btw was a flat-out lie, because I was in the alpha and the response was overwhelmingly positive and the actual developers came forth and stating it was corporate shenaigans that caused the cut, they literally one day went to work and found the studio closed!)).
Likewise RTS games are a niche-genre nowadays. With nearly every developer jumping through hoops to attract more players (and in imho too many cases doing that by reducing difficulty/challenge and skill gates (the latter mostly in multiplayer games)), players that are willing to spend countless hours experimenting with different build-orders, learning a dozen maps inside-out are in rare supply, hence not exactly the most profiting target audience.
RTS itself is very much kicking, CoH proved that and even SCII which is basically just a graphically reworked SC is obviously a monster in the RTS genre (which obviously likewise deters potential developers to try and get a market share seeing how they'd be going up against a longstanding franchise with a giant fanbase), but it simply isn't mainstream anymore. If a game isn't mainstream enough, publishers are hesitant to throw money at it, hence making it hard to try and make something big and new.
The entire Total War Series(amazing mods for Medieval Kingdoms, namely Stainless Steel) , Europa Universalis, Crusader Kingdoms, Galactic Civilisations, Civilisation series, Dawn of War series, the incoming Battle Fleet Gothic fleet battles, Mordenheim, sins of a Solar Empire.
If you want to stretch the definition. The Banner Sage is awesome, XCOM both enemy unknown and Within with the Long War mod it's soooo punishingly good, Prodigy a table top/turn based game.
Many of the games you named aren't RTS ... the only RTS I see are DoW, BFG and SoaSE.
And games like Banner Saga and XCom are by no means RTS, however thin you intend to stretch the definition.