Main reason: Dutch are so well insured, we can't imagine costs being so fastly different abroad.
Second reason: We Dutch are cheap as hell, and we will cut costs where we think it's possible.
And no, it's not "poor" folk who this happens too. Poor folk don't get to go abroad. Plus a continuous travel insurance is like €2/€3 euros extra a month on you standard insurance.
https://nltimes.nl/2024/08/09/medical-costs-abroad-getting-dutch-trouble