Safety standards, build and material costs, and fuel efficiency requirements happened.

This isn't necessarily a bad thing. And it's certainly not limited to Mercedes. Do you like your modern cars to get good mileage, but still have modern conveniences? They need to weigh less. Want to be safer in a crash? They need crumple zones. Want to be able to afford a car? Then it needs to be made from less expensive materials, and fewer of them.

To meet expectations, cars need to be more refined and engineered. Instead of building things heavy and strong, they need to be engineered to use the fewest resources, but those resources need to be just strong enough to do the job.

There was a crash test done a while back between a 50's or 60's piece of detroit iron and it's modern equivalent. Very thought provoking.