It is worth saying that this is changing at the edges, and where it is changing tells you the trade clearly.
Single-ring setups are common on gravel bikes, where the terrain is rougher, chain retention matters again and riders accept bigger gaps. They appear on time trial bikes, where the range needed is narrow so a single ring can cover it with small steps. And they show up on commuter and utility bikes, where simplicity and low maintenance beat perfect cadence.
What has kept them off performance road bikes is that cassettes with twelve or thirteen sprockets still cannot deliver both the range and the spacing that two rings give. As sprocket counts keep rising that gap narrows, and the transition may well happen eventually — for the same reason it happened off-road, once the compromise stopped costing anything.