I think packaging of where to locate everything without having to cut the car up is high on the list.
With turbos, your looking at custom plumbing, and I din't think there is a "bolt-on" kit for DIYs who don't weld.
I think the Blower engines are more common because they are easier to "bolt-on", and remove or cut the hood.
Then there is the cost, and the market segment.
A big part of the market seems to be restoration, or semi-easy and reversible bolt-ons.
For turbo engines (and Hellcat engine), I think if an owner was to goto the expense it might be towards GenIII hemi-swaps with forced induction.