Amsterdam is built on wooden piles
Do you not mean Venice? Are the canals of Amsterdam not dug out?
Either way - by all means correct me on the above, you are simple not comparing like with like.
The only country that has invested significantly in entirely off-shore airports is Japan. Kansai in particular shrunk far more than was anticipated, and don't get me started on the costs of any of these facilities.
Yet, we do actually still have the land to build elsewhere.