The European allies have put their money and more importantly blood into these conflicts.
Yes, we can all look at a geographical map and state that the USA is blessed geographically by being split by two oceans from anything major in the world and thus conclude that the US does not need Europeans to defend its borders.
In essence you're completely ignoring how US allies in form of NATO allowed US to thrive as the global military power by providing a deep web of support, logistics, bases, ports, intelligence and allowing the US to have a huge influence it has consistently leveraged for decades to its own benefit or needs. And that includes financial reasons (like buying US weaponry).
If US wants to pull out of NATO it is what it is, but this whole nonsense of NATO benefitting only the European allies when it's always Washington asking for other's blood and bases and logistics is just it: nonsense.
