Chess presents a comparatively small and, importantly, discrete set of choices at any moment. So it feels like it's a solvable logic puzzle: like it should be possible, at any moment, to make an optimal move. You can predict if you lose 2 or if you lose 3 pieces because of your next move, and you're expected to use this knowledge. The strategy of chess is about perfection in every turn.

RTSes present continuous, large choice spaces. So it doesn't really feel like as much of a logic puzzle, and perfection does not appear to be within ones grasp at every moment. Whether you'll lose 4 or 6 of the T2 fighter-bombers is not relevant. The strategy of RTSes is strategy of big plans and high level abstraction.