Is this a conscious decision that manufacturers have made not to include such feature, so that photographers can be aware of the HSS flash power limitations?

In my opinion, yes, I think this is why it's usually implemented the other way around: that you have to turn HSS on, and then the camera only stops using HSS if the shutter speed falls below sync speed. Otherwise, the shutter speed stops at sync speed with flash. The shooter needs to make the conscious decision to trade off a -2EV power drop for the faster shutter speeds with HSS.

Given that speedlights are the lowest-power strobes you can use, often using one effectively is about using your power as efficiently as possible. For some folks, say wedding shooters who need faster recycling, a safety rail keeping them out of the HSS "power-suck" zone may be a feature, not a bug.

Implementing it as you suggest, as an auto-switched mode based on shutter speed is likely to result in a lot of very confused shooters wondering what's wrong with their flash when they didn't change any flash settings but suddenly lost two stops of power. Without HSS set, having shutter speeds max out at the sync speed forces shooters to be aware of the sync speed "border" and to make the decision to cross it.