Lack of seatbelt, lack of curtain air bags, and relatively poor roof strength of the older truck.
A high speed side impact is probably the worst kind, even if you survive the chances of serious injury is nearly unavoidable. The truck was hit from the passenger side, the driver's body would be violently tossed towards that side. With no support in that direction (head rest, airbag), serious neck / back injuries are likely.
If I had to pick a vehicle to be in, it'll be a modern large SUV with tons of airbags and strong roof structure (the Ram looks to have caved in a bit). Most modern SUVs and trucks can support 4 to 6 times their own weight on their roofs.