RTS is not a very popular genre all things considered, and the ARTS/MOBA variants are dominated by DOTA and League of Legends.
You also can’t play RTS games on consoles.
A lot of fans of StarCraft still wish they saw StarCraft: Ghost see the light of day. Arguably the franchise is very much underdeveloped. The IP and story would work well for many game genres that haven’t been explored.
If StarCraft 3 comes out it would only be popular in South Korea and possibly not all that popular at all even there.