Amsterdam, specifically Science Park, is basically the biggest internet hub in Europe. Frankfurt is second. A lot of stuff is there. It also helps they don't have overly strict policing like in Germany.

Sure, but even if a provider peers through Amsterdam it doesn't mean their IPs must be geolocated and registered there. It's probably because of favorable legislation.

Also some car entertainment systems with integrated 4G/5G use Dutch IPs. Which leads to the weird situation that I sometimes get dutch radio ads on TuneIn or some websites redirect to the Dutch version.