- RTS games, since the first C&C, used an interface for selecting rectangles and pointing them at a single target. It scales extremely poorly. Innovations in this area have failed to catch on. Keyboard used for shortcuts only. Come on, we can do better than that. We have Vim. Action, range(movement key). Alternatively, the Kakoune way: selection first, action second. Either way games lack a fast way to select only certain types of units, and especially - to point them at targets of certain types. Harvest: Massive Encounter is a low budget tower defense games which allows you to set targetting priorities for each type of your tower, but RTS games need much, much more systems like that.
Meanwhile Starcraft has been busy embracing and glorifying primitive user interfaces. It has its caveman charm, but - by design - it scales only by clicking faster.
- RTS games were popular at a time when computers were predominantly used by nerds. RTS games appeal mostly to people willing to get better at a game. Publishers discovered less demanding games sell better.
- RTS games are highly demanding to make from technical point of view. You get all the joys of pathfinding at large scale. Optimizations are very important.
- RTS games are not that immersive. This is true for all "topdown" perspective games.