It's an unfortunate side-effect of our times. The big money just doesn't lie in RTS and TBS games, so the big studios can't really be arsed to make them. Look at how many people are excited for BF4 and then look at how many people were excited for one of the more popular strategy series, Rome 2 Total War. The number simply cannot compare.

It's really sad, I absolutely love strategy games. I prefer TBS though, and luckily we've recently seen a pretty big increase in the amount of TBS games being released, albeit mostly from niche and indie developers.