Not exactly true.
Older 35mm movie content is being scanned by the big studios at up to 16K. I remember watching this on an episode of "Click" on BBC News 24 a couple of years ago now, so perhaps they are going even higher now (if that's needed?).
I've been watching Star Trek - TNG again, which was filmed on 35mm and completely re-mastered for BlueRay release and it is stunning.
Aside from the 4:3 and film grain, this TV show still looks modern