RTSes were never meant for consoles, originally. Saying that they require a keyboard and a mouse is like saying that they should have been made for consoles, but that the RTS decline is due to the fact that most console companies almost never produced (at least officially) a keyboard and a mouse for their system (I can only think of the Dreamcast right now which did have those, I know more did too but it's only been a few select). That doesn't quite make sense to me. If I'm a game developer wanting to make an RTS game, I won't make it for a console and then cross my fingers that the company responsible for the platform I chose to make the game for will happen to also make a keyboard and a mouse for it. And if they don't, then I'll have to hope the game audience of that system will be content playing it with the system's controller. No businesses, no devs would rely on that to exist.
The problem isn't that RTSes require a keyboard and a mouse. The problem is RTS makers made the choice (or publishers did, whichever way) to leave the PC platform in favor for consoles with the prospect of making more money because the assumption was that the audience(s) on those systems was bigger. They never thought about the severe consequences of a completely different interface to interact with the games would provoke in the genre. They just thought about the money and did very little to absolutely no forward-thinking ahead of time. It was, ultimately, in the hope to make more money because even if RTSes started on, and became popular on, and because of the PC platform, they were relatively still a niche thing by comparison to how much money other "Console exclusive IPs" were making in the meantime. I think that Nintendo were happy swimming in their Mario money, while Westwood had to work their ass off with C&C2 and hoping it'd work well enough to keep their job.
I'll never blame consoles, or the "dumbing down" of society for the decline of RTS gaming in general. I'll blame the publishers and/or the developers who simply left their original established and comfortable platform (PC) in favor for the consoles. It was their choice. I do NOT know a single console gamer who ever wanted Command & Conquer on the N64, to use just that example. About as much as I've never heard a single purely PC gamer ever saying that they actually wanted the Zelda or Mario franchise to come on PC (excluding emulation). And no console gamer uses the argument that those franchises never came to PC because they 'require a controller' (which has been a type of peripheral we can get on PC since... I can't even recall because it's been there for way too long by now).
The PC platform had "its own things" (games, genres) that consoles didn't. The PC platform had RTSes and action RPGs just to name those two (also Flight Simulators and so on), the consoles had their Platformers and their Beat 'em Ups. But consoles grew up in popularity with the arrival of the NES, the market "share" of consoles Versus the PC for video gaming massively increased; of course in favor of consoles, because hey... remember how much it cost to get a good "gaming PC" back then? Exactly. The publishers (surely) and at least some developers of course saw that happen, and the scent of money coming their way made them make some pretty stupid decisions in the name of business and profits. The mistake wasn't exactly to 'just go' with consoles and their RTSes in an attempt to 'bring the genre' over to a new audience to make more money. The one big mistake that corroded the genre over time was to LEAVE the PC platform almost entirely, instead of doing both. It's been only very recently that we've seen a very small humble and almost silent 'return' of RTSes on PC, thanks to the sudden surge of "Indie" style development teams being able to experiment and do whatever they think might work on platforms that didn't exist the way they do right now, barely 10 years ago, such as the Steam Early Access system. Games like Grey Goo wouldn't have been remotely discussed internally anywhere in the industry just 10, 12 or 15 years ago. It would have been deemed a failure by the big companies that the 'daring' teams would have relied on to publish their games.
Nah, requiring a keyboard and a mouse isn't a problem; if you make the game for the PC. No one is asking for RTSes on consoles. So the keyboard and mouse requirement thing I just cannot agree with. Heck, there's more market for RTSes on mobile than there is on console, especially nowadays. Kids today want to play Fortnite and more generic FPSes (generalization aside the gist of the idea is there; I am still a console gamer myself, I'm not just a kid anymore and I hate Fortnite, but I do NOT ask for nor want an RTS on my Wii U, and will not ask for anymore RTSes by the time I get my Switch specifically for Super Mario Maker 2). No one there is asking for, much less caring about the future of Command & Conquer or a return of Dune, or the sequel to StarCraft 2.
If an RTS comes out tomorrow on PS4 and isn't popular because it 'requires a keyboard and a mouse', then the problem is the platform it was made for. And I put the blame on the publishers and/or developers (or whomever made the conscious choice between them, or both of them).