As far as I'm aware, high speed drones tend to have quite short flight durations due to battery limitations. Drones that have the range to follow a fleeing suspect for a long time would probably have to be big enough that they could cause a fatal accident if they crash, and in that case I'd rather have a pilot on board. Better reaction time, no risk from jamming, much better field of view/awareness, decades of testing, etc.

Most of the small high speed drones are that size to fit under professional licencing requirements, often so that one racing spec can be viable across a wider area. Leading to significant competition in that size pushing down prices.

Rather than some inherent sized for safety idea.

Jamming might be interesting, I suspect that it's easy enough (and a much bigger crime) to follow a very loud jamming signal though.

Every practical metric a drone surpasses a helicopter; they are so much simpler to operate that you can easily offset any perceived downside with more drones. And you don't get a tested solution without trying it out.