I think that’s down to formula e being very-nearly a spec series. Formula e fans get very defensive it not being a spec series, but the regulations (and lack of big time money) make the cars much, much more similar than they are in F1.
The powertrain is pretty free nowadays in Formula E, but the rest of the car is almost entirely spec, which inevitably means there's a lot of similarity. It also means they can spec something where the aero doesn't produce so much dirty air.
I think keeping the development limited to the powertrain is the right move for Formula E; there's plenty of other series where money is thrown at the rest of the car, so let developments happen where the series stands out.
