Not quite true, the RTS is really a popular player genre. but not popular with major publishers. Because the "game service" concept with lootboxes completely captured the minds of publishers. They want to create minimal content but sell it for maximum profit. RTS can not squeeze money out of players as much as possible. Therefore, the RTS is not so popular for development.
We don't need to lie to ourselves. This is not the 90/00, golden time for RTS is far gone.
STRATEGY, as a general category, is popular. But that's because it includes way too many different genres which are not close to each other. RTS, RTT (MoW), TBS (Civ), TBT (Xcom), Artillery, Tower Defense, MOBAs, etc.
RTS outside of having big fanbases (Starcraft, Warcraft, Age of empires, CoH) is extremely niche. The genre requires heavy time investment in order to start to scrap the real hidden value of the product, something which the masses are not going to do.
That's why MOBAs replaced RTS, at least in terms of PvP demographic. They are easier to start with, even if the skill roof is still high.
Any news about COH 3 ???
Forget about it, at least for 4/5 years more. Relic is currently busy with AoE4, which you can't expect to get any fresh news till end of year or way into 2020. If they are still assigned to the IP for post release content, you would still need to wait even more.
If you can't wait, the closet thing you could get is Iron Harvest.