If you saw the ones on my mom's 94 Nissan Sentra, you'd see they're totally busted now, and the rails are only made of plastic, which long ago dryrotted and now the guide cables are just randomly hanging out and neither side works anymore.
Hell, even when they were brand spanking new, do you really trust your life to seatbelts only held in place by fucking plastic tracks?
Plus you still gotta manually latch the lower lap belt, which most people totally forget even exist when the shoulder belt is automatic.
That's like the most dangerous form of seatbelt to have ever been made. Thankfully that shit rightfully died out, the OG 3 point seatbelt invented by Volvo is by far the best.
If you want photos of my mom's damaged seatbelts to better understand, just message me back and I'll see about getting and sharing a photo tomorrow or soon. It's fucked.