If the US pulls out of NATO, then it's true that Europe has very little reason to support American interests (unless America "pulls out" of NATO by renegotiating a new mutual defense pact, in which case the countries in that treaty obviously will have plenty of reason to support America — similar to how Trump replaced NAFTA with the USMCA in his first term; which is also what Trump has said he wants to do with NATO).
However, that is an "if" statement that has not come to pass.
Well, threatening to seize an ally's territory kind of put the ally bit in question doesn't it? For all intents and purposes NATO ended existing with Trumps speculation to use military force to seize Greenland. After that statement nobody can consider the US a reliable ally anymore. So.. the US may not have pulled out of NATO^ but there is absolutely no reason to believe in any kind of support being available from the US either.
^which by-the-by is difficult to achieve on a practical level. Notifications of withdrawal have to be handed in to the US government
If you were correct, then European countries wouldn't keep asking that the US sign an agreement to backstop a Ukraine deal — after all, regardless of the paper, the US wouldn't be trusted to do it.
But they are asking for that; I think you should consider why.
However, that is an "if" statement that has not come to pass.