Because it is! Looking online it looks like prices in this area are around €250k for a 400-600 sqft apartment. It looks like land just outside of this area goes for ~€200k for 0.2 acres, houses go for around €500k - 1.5mil, and townhomes go for around €200k. Rents in the area are fairly affordable at ~€475 per month (one bedroom city center) but the average salary is only ~€950 per month. Also the population is only ~15k.
The person who made the post in the image is comparing apples to oranges. My small-ish US town has a population of 10k and you can get 3 acres of land and a 2000 sq ft house for $250k. Gas station and grocery store are 10 min down the road by car. The average monthly wage is $3400 in this town.
Basically, the average person in the pictured town would need 22 years of their full salary to pay for a townhome while the average person in my town only needs 6 years of their full salary. The American mind may not be able to comprehend this picture, but it's not like most Croatians can live there either.
I mean, Rovinj is as much the sticks as my town, it's just old and on the water. There's almost nothing there and it's only popular as a tourist destination. According to Wikipedia cars are the primary form of transportation outside the area in this picture and it's quite far from anything else. Also according to wikipedia much of the small businesses in this area shut down in the off season since it's mostly a beach tourist area. The closest major city is Pula (population 52k) which is 45 min from Rovinj. In comparison the largest city in my state is 25 min away and it alone has 20% of the population of the entire country of Croatia. All that said and living in old town Rovinj is less attainable to Croatians than my example is to Americans living in my area.
Care to elaborate? I listed the average wage for the city in my original post and the average wage for all of Croatia isn't much more (about €1100/month). Spending 40-50% of your pre-tax income to rent 400 sqft doesn't seem like a great deal to me.