A lack of need for innovation seems to pervade successful RTS games, both currently and historically. Starcraft established a trend that Blizzard capitalised on with Brood War, making an expansion that defined multiplayer RTS gaming for a generation (or more, effectively). Nobody really even recalls Warcraft multiplayer outside of some truly memorable mapmods. At least, nobody on a scale compared with the heights that Brood War manages to reach even these days (complaints about how Blizzard have mishandled SC2 aside, for today). However, this very success warped a lot of perception around what a good RTS should be, from both the perspective of management (in the games industry) and from the consumers - the players themselves.
I did warn you that this was all my opinion, and not necessarily fact? Good. Worth repeating.
However, this lack of innovation is also due to two factors.
One, the "niche-ness" of the RTS genre. Nomatter how you cut it, or try to argue it, when compared against other major genres in video games, RTS is niche. RPGs are huge, and translate to the console markets well. FPS (and TPS) are, well, they speak for themselves. Halo defined a console generation. MMOs leverage a huge customer base (if successful, and you simply don't really hear about the failures), and a lot of the time also leverage the popularity of the RPG genre with regards to design (hence MMORPG: I'd argue the only majorly-successful MMO that isn't a strict RPG is probably EVE? Maybe). RTS games do not require a huge amount of people in order to sustain themselves. I can still play Warcraft 3 on my PC and have a good time. I can even play it with friends. But they're not huge. They don't translate well to consoles. They require a base skill level only really found in the up-and-coming MOBA genre (another one I'm actually heavily-invested in, funnily enough) - however the MOBA games leverage both an existing fanbase that grew out of nowhere and the attraction of a primarily-F2P-monetised genre.
On that note, an F2P RTS venture could be interesting if microtransactions were handled right - I feel EA cancelling Generals 2 was a bad move, but unfortunately made necessary by the extremely volatile reactions of the fanbase.
Two is the success of existing behemoths. Much like how WoW dominates the fantasy MMORPG space (very effectively, and while I dislike what they've done with it personally you could never say that Blizzard don't put out good stuff on a number of levels), Starcraft is the go-to example for RTS games. You can't compete with it. There's no point even trying, because Blizzard let the community polish Brood Wars to a sparkling gem and then pushed out their specific brand of "sink a billion pounds sterling of polish into the sequel" because that's what Blizzard can afford to do. And yet companies try to. The focus on eSports for newer RTS games (the focus of which split Dawn of War II in half, even if I think the design goals at the time were visionary. But perhaps too visionary back in 2008 - 2009). The notion that games have to compete with Starcraft 2. The notion of capturing the SEA market.
You combine these factors and not only do you have a mindset that is averse to change (the gamers won't accept it, and therefore management won't risk it) but given the nature of video games development favours making money (it's a business, I never judge developers or publishers for prioritising this, unlike other gamers I know - unless the company is explicitly taking the piss) new RTS games are therefore developed. So you get Grey Goo, which is a fantastic-looking game with a great pedigree behind it . . . but at the end of the day it's still a very typically-designed RTS. Planetary Annihilation breaks several moulds, but for me that's the exception that proves the rule, haha. Company of Heroes 2 is a great game (and I like it more than the original), but it's quite obvious that the backlash to Dawn of War II changing the traditional RTS formula caused Relic Entertainment (or THQ) to go back to vCoH and not really rock the barrel too much with regards to innovations. Which is a crying shame, because Relic are I feel excellent at making innovations. Absolutely excellent.
Sync kills are amazing. Sorry, this picture doesn't get any bigger.
My RTS knowledge, unfortunately, is lacking in some areas. I never played Ground Control. Or Earth 2150. Or a few others that are knocking around. But I have a good knowledge of Command & Conquer, Company of Heroes, Homeworld and obviously Dawn of War. I backed (and play) Planetary Annihilation. I definitely like the genre, but I feel there's a distinct lack of innovations driving it forwards.
However, this doesn't mean at the same time these innovations can magically happen. I was going to wax lyrical about how resource systems in RTS games haven't changed but I focused a lot on the business-side of things with this blog post, so maybe I'll get around to mechanical arguments next time. I'm a developer after all, making games on the side. The technical / mechanical side of things is what I love more than anything else.
Well, if I don't get sidetracked making more modifications for Firaxis' brilliant new Civilisation: Beyond Earth (sod the haters) :P