VGChatz’s Taneli Palola: “There’s no question that during these years the overall popularity of the genre took a significant hit, as most games within it specialized even further by adding new elements from other types of games into their gameplay loops and consequently became increasingly niche as the years wore on.
However, this doesn’t in any way mean that the period was devoid of great games. Quite the contrary, in fact. Arguably some of the greatest RTS titles ever made came out around this time, and much of this was because many developers were increasingly familiar and comfortable with adding new twists and gameplay elements to the familiar formula. As such, even when the genre’s popularity dwindled, many studios were still creating excellent and groundbreaking titles almost every year, just for a smaller audience than in years past.”
Source: N4G PC History of Real-Time Strategy: The Downfall (2004 – 2010)