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.