After depletion of the reserve capacity, a jump will get you a couple minutes at best. These aren't "brainiacs" who know what's going on . . look for the tow truck, it's coming. OH . and if it's night time, you're going nowhere
Funny how you say it can't be done when I've done it. Multiple times. A revved up 3G alternator can juice up a dead battery for folks pretty darn well from my experience. I carry big fat welding lead grade jumper cables. I've gotten more than a few people off the side of the road. A couple of times it was me on the side of the road. I've driven a lot of low quality vehicles over the years.
I once limped a motorcycle home 20 miles that wasn't charging. The last ten miles it was so weak if I touched the brake lights the engine would sputter.
Another different motorcycle quit charging at night miles from home out in the boondocks. I puttered along in the dark with a pocket flashlight but turned on the running lights when a car came along.
A friend and I once hot-swapped batteries in running cars so the one not charging could keep going. Took three swaps to get home. How we didn't blow the charging system on the good car, I don't know but it worked.
To get a trail bike out of the woods we once rigged up a household extension cord and plugged the ailing bike into a second bike. Then both riders stayed side by side and rode back to the trailer. Ruined the extension cord for its original purpose but I kept it in my bike bag for years after. As I recall when we were rigging it up a bystander was there insisting that "That'll NEVER work."
Just because they don't teach this stuff in school doesn't mean it doesn't work out in the field.
My priority is to get folks the heck off the interstate if I can, using whatever tools are at hand. It's very dangerous on the side of the highway. If jumping them off will get their car a couple of miles to an exit I'll try it. Sometimes I drive a tow truck too but I'm only after highway patrol/county/city calls. Wrecks, DUI's, and such.