Real-time strategy dominated a period of PC gaming and then largely stopped receiving large productions. Several unrelated pressures happened to point the same way.
The skill being tested became execution speed
Competitive play rewards issuing many correct commands quickly, because a player who can manage more units in the same interval simply achieves more.
Over time the competitive standard rose until the mechanical demand outweighed the decision-making, and the genre's identity as a thinking game sat awkwardly with that.
New players encountering it discovered that understanding the correct strategy was not enough to execute it, which is a discouraging place for a beginner to be.
Adjacent genres absorbed the appealing parts
Controlling one unit in a persistent team match, which grew directly out of custom real-time strategy maps, kept the tactical decisions while removing the management burden.
Turn-based strategy kept the planning and removed the time pressure, which suited players who wanted the thinking without the mechanical demand.
Both attracted audiences that would previously have had nowhere else to go, and the remaining core audience was too small to fund large productions.
Production costs rose faster than the audience
A real-time strategy game needs many distinct units, each animated, voiced and balanced, along with a campaign that is essentially a series of bespoke levels.
Unit counts that were achievable when assets were simple became very expensive once fidelity expectations rose, and none of that work can be reused as easily as an open world's terrain.
Publishers comparing that cost against the likely audience have generally concluded the numbers do not work, which is a commercial judgment rather than a creative one.
Console and touch platforms never fitted
The genre depends on rapid precise selection across a large space, which a mouse does effortlessly and no other common input device does well.
Excluding consoles removed the market that justified large budgets elsewhere, leaving the genre dependent on a single platform.
Attempts to adapt the controls generally simplified the game enough that it became something else, which satisfied neither audience.
The genre persists at a smaller scale
Independent studios continue to release real-time strategy games, often built around a specific idea rather than trying to reproduce the full scope of the earlier era.
Automation, simplified economies and slower pacing appear repeatedly, all of which reduce the mechanical demand while keeping the decisions intact.
Whether that constitutes a revival or a redefinition depends on which part of the original appeal a given player valued most.