Because it is the fate of any activity that a higher intellect can easily program for automation.

It will return once a developer realizes that these automatons, though superior in low thoughtform, can be accounted for and gamified by allowing higher thoughtform (humans) to control them enmasse across much larger battlefields.

The barrier to entry for programming a relatively effective CPU that can attain a high ELO rank is low, so the population that would in the past be interested in RTS have gravitated on to grander schemes.

So, age of empires for example: 1v1, you will never beat a properly programmed CPU. But assail that CPU with a rival of itself, burdened with an exponentially larger computational surface area the size of a continent or planet, while slowing down time and relegating the player to a more handsoff advisorial role specialized in 'grand scheme of things', should sufficiently handicap even the best current AI, while exemplifying the superiority of symbiotic of AI micro-ing commanded by the intangible thing that is true sentience.

TL;DR: Lonely AI versus AI advised by a sufficiently high IQ human = ?

But this too will be mirrored and parroted and clonified, ever continuing the IQ arms race