They used the biggest modules they could fit in a Shuttle. Or fit in a rocket fairing if they could fly themselves. That meant being stuck with 4.5m wide cans. The old Salyut stations were single modules, then MIR was a big modular one to get more space, crew, power, equipment, etc, and ISS is the evolution of that idea.
Skylab was a huge volume because they used a Saturn upper stage. Some new stations will have bigger single modules, like Orbital Reef and Voyager, because of the bigger fairing sizes on Starship and New Glenn. Inflatables are a little annoying to build out inside and they still need some dev work, so a lot of the next gen stations are big cans that might have some inflatable modules on the sides.