>> instead they blew it and used a super-high-RPM motor-powered narrow turbine placed inside the pipe.
Because it is a handheld tool. It cannot be heavy. If you want to shove lots of power through an electric motor then that motor has to be either very heavy or very fast. The same is true for turbines. And a lighter consumer product will generally be cheaper to manufacture.
Another reason for smaller and lighter fans is the lower moment of inertia, which means faster spin up and spin down. Unfortunately, these frequent spin ups annoy me to no end.
Because it is a handheld tool. It cannot be heavy. If you want to shove lots of power through an electric motor then that motor has to be either very heavy or very fast. The same is true for turbines. And a lighter consumer product will generally be cheaper to manufacture.