I mean, the bench is painted. Paint isn't usually known for being an electrical conductor. While conductive blends exist, I don't think they'd be very viable nor cost effective for an outdoor application such as this. That's just speculation though. There are also the safety and liability issues with something like this, for insurance if the electricity were turned on by accident during hours it should be safe.

If a city government can pay $20k extra per unit to ensure it causes needless suffering to homeless ppl (and get away with it), I wouldn't hold my breath on them not spending it. That said, we should probably reserve our ire for actual anti-homeless atrocities committed by PDs and city councils. Art projects making an apt social commentary are thought provoking but should be recognized as such.

Of course, as you mentioned it's entirely possible something like this exists already. I haven't seen any proof of that, but in such a case it would probably be easier to just not paint the bench and leave it at that.