There was a demand.Gun makers meeting a demand, or trying to create one.
LE agencies responded to the need for higher capacity guns than 6-shot revolvers as they felt underarmed by asking for semi-automatic pistols. They also bought into the belief that the DA/SA pistol required a trigger finger shift and two divergent techniques. The closest trigger action to that of the revolver they had the most experience with as a DAO. The first examples were less than optimal, but technology has caught up with the Sig DAK and the H&K LEM...which are very revolver-like