Ah sure, the vets are obviously lying about the dogs that have come in and died as a result...
Dogs in countries that are reliably and predictably hotter tend to be better acclimated, haven't still got a massive thick coat (Which two out of three of my dogs needed just a month back) and are generally much more used to managing dogs in the heat.
Quite crucially, in other countries they either have aircon or they have houses designed to stay cool in hot weather. We have neither, so your overheated dog comes home from his stupid walk, and into a hot house ... and still can't cool down rapidly, or usefully.
And dogs do still die in other countries, its not as if its ONLY here!
The 20c in the car - you realise that in 10 minutes its heading over 27 in a car parked in full sun, windows down or not.
Time yourself next time you hop out of the car to nip into a shop, chances are you think you're five or ten minutes and you're easily double that.
Most people do not have a car with a dog-mode aircon system, so to leave the aircon running they need to leave the engine idling which isn't legal here.