You can't really take the one of the most visited and touristy places in Croatia and consider it the average.

By comparison the largest city Zagreb of about a million people, which is a quarter of the entire population, has the density of 1300 people per km2, that's about 1/3 or 1/4 of the pop. density of Berlin or Stockholm.

Compared to Norway which is the least populated country on the continent, Croatia has the same population in 20% of the space.

But it's not just tourists. I had an internship at the uni in Split, and that thing has like 10 floors.

That's because of atrocious urban planning. Traditional Mediterranean streets were never meant for cars. Municipal governments, instead of having a clear strategy where historic city centers are preserved and everything else is bulldozed to make room for proper, modern urban design have instead opted to have no plan whatsoever. As a consequence, there is now nowhere to park, the streets are hard to navigate (even for locals) and things like sidewalks and bike lanes are pure fantasy in many of Croatia's coastal cities.

Car oriented cities are a bad idea.