That because only one company actually has any vested interest in a pure RTS, and that is Blizzard (sadly Blizzard Activision now). Starcraft 2 is doing pretty well, all things considered, particularly with F2P. Warcraft 3 is being remastered this year and will no doubt do pretty well. It takes an awful lot of resources to make a balanced RTS at the level of SC2 and I just cant see any other company having the incentive to do so, Blizzard do it because of the heritage of Starcraft in esports. With the recent goings on at Blizzard though who knows, Starcraft has been confirmed for this year in terms of esports investment, and the warchests (paid cosmetic content) that they sell continues to sell out every time, but the reality is that whilst it is the pinnacle of a genre it doesnt make the kind of money that they could make by diverting those resources into some other area *cough Battle Royale*. The Diablo mobile guff was just a small taste of what is to come in all likelyhood, but here's hoping that RTS's can hang on somehow as they are a founding pillar of PC gaming, and even more so, esports gaming.