Thing is the motors are not just about outright power - for me the Shimano is still the most natural feeling motor of the bunch, that mimics how you interact in terms of cadence and pedal inputs to that of a regular mtb, and on top of that the Shimano is probably the easiest system to integrate into a frame design without having to make compromises which is why a lot of brands go for it.
If you are looking at making a great riding and handling bike, then the shimano is still first choice for being able to do this.
On top of this the relatively large amount of customisation of installation and component choice within the steps eco system - if I was a designer at SC, Pivot or Yeti the bar warts and spider web of wires that make up the Bosch controls would put me off alone from gracing my bike!