StarCraft hasn't seen any significant development since 2015. There aren't many other competitors in the RTS space since about that time, as well.
C&C hasn't had anything since 2010. AoE's last major entry was in 2021 and had a pretty weak reception. I can't think of the last RTS that actually sold well and has large adoption besides SC2.
It's a very niche genre these days, and few developers are willing to make them in today's climate of looters, extractions, and battle royales. RTS games just simply aren't making the waves they used to anymore.