The RTS genre "didn't die", game developers lost their imagination. The reality is RTS games had serious design flaws. The rise of so called "moba games" (aka rts games with one unit you control in pvp /w rpg elements).
Moba's are basically single unit RTS games that you pvp with other players with. People want to be attached to their fighting unit when pvp'ing, games like supreme commander you're looking down at icons from orbit so you are taken out of the action. Supcom is everything that went right and went wrong with RTS games. All the sides in supcom are prettymuch clones with no interesting properties. Air dominates on large maps, sea units are mostly useless. There's tonnes of redundant units.
RTS games as a game design are caught between full blown action games and more slower turn based affairs but does neither well.
Dragon commander was an interesting experiment in combining small civilization 4x with really super basic rts. It was the greatest idea poorly executed nobody played because the game was unfinished.
https://www.gog.com/game/divinity_dragon_commander
"MOBA" (I hate that term) is just code for warcraft 3 hero arena/dota gameplay mod type games. They are just one or few unit rts games.
I really hate league of legends/DOTA F2P because you can't add maps, custom characters or anything because the games are locked down. They are basically where RTS went - down the drain with the rise of the next generation of gamers, most gamers are too reflex challenged and dumb to handle more complex RTS games. Which is why RTS is on life support outside of say starcraft.