Having the same currency as your tourists (mostly people from the north, to a lesser extent people from the east and northeast) helps a lot.
Schengen helps also, but even before people could just drive there without noticing the border.
No passport control at the airport is also a nice bonus. I can’t describe that feeling when I travel to another country without going through border checks, it’s so liberating.
Not during the summer. There were usually big queues at border crossings during every summer weekend. This should alleviate that a bit - the pressure will just move elsewhere in the road network, but will hopefully be easier to manage.
Long queues and passport checks every time.
So if what you say is true and you can drive without noticing the border there must be some bias.
Possibly depending on which country of the Schengen zone you're entering Croatia from.