The empty space in older cars is definitely a big contributer to how much simpler it was to work on them. Plenty of project cars I owned or worked on that had more than enough room in the engine bay to actually STAND inside between the frame and engine with the engine / wiring / hoses still present and both feet planted on the ground.

Much less daunting and convenient to work on an engine or replace a part when you don't have to take off (and potentially break) a million other parts to get at what you want to replace and you actually have the room to see what you're doing instead of blindly groping around for something vaguely shaped like something you've only seen a picture of.

That and the absolute sheer amount of electronics in modern cars. Older cars had the absolute bear minimal amount of wiring to the point that it was entirely plausible to more or less keep the wiring schematic in your head and even (speaking from experience) redo the entire wiring harness front to back on your own with a few different colored rolls of wire from a hardware store yourself.

I can't imagine how people getting into the hobby now with newer cars feel looking at the unholy mess of endless amounts of wiring, sensors, mechanical parts all jammed together in tightly packed space efficient layouts probably designed by someone purely working on them in a digital space. On the bright side at least they have youtube and better resources on the Internet to look up how to actually do something though.