Unfortunately the train routes from the Netherlands to, say, Portugal, Spain, Italy, or eastern Europe are not well developed enough yet. The train is great in the directions of Paris, Frankfurt, Berlin, and London, but beyond that it often takes longer than flying and often requires multiple tickets
You just describe when it’s convenient not when anyone needs to fly. With the same reasoning everyone needs to use a car for everything outside a 500m radius because it’s faster than going by bike.
I regularly hear people say stuff like “I would like to take the train, but the flight was cheapest”. “You know, i’d take the train, but with switching twice and 8 hours… and the flight was only a bit more expensive”
There is still a lot of convenience over actual need.