I know NOTHING about cars but why is that? Is there more "stuff" under the hood today?
1. Since old cars were longer and wider, the engine compartments were bigger and it was easier to reach around the engine to work on it.
2. Old cars had longitudinal-mounted engines. Meaning four cylinders were on the drivers side and four cylinders were on the passenger side. Changing spark plugs or doing cylinder head work was easy to get to. The engine shaft that drives all the belts exits the engine toward the front of the car, so everything driven by a belt: alternator, power steering pump, water pump, A/C compressor are in the front of the car and easy to get to.
Most engines now are transverse-mounted meaning three cylinders point to the front of the car and three point to the back of the car hidden under the dashboard. Changing spark plugs or doing cylinder work on the side of the engine that points back is a bear because you can't see what is back there, you have to feel around for everything you want to work on since you can't see it. The shaft coming out of the engine points sideways toward the passenger side of the car. Everything driven by a belt are a couple inches from the right fender. Hence I had to drop the engine down below the fender to access the water pump bolts.
3. More complicated engine design makes accessing components more difficult, Example: old days the carburetor was mounted on top the engine. Now fixing fuel injectors requires taking the throttle body off.
4. Engines now are sometimes harder to get to due to plastic panels at various places to help aerodynamics. For instance something as simple as reaching an oil drain plug requires removing a plastic panel underneath the vehicle.