No it's because we survived 2 VERY destructive world wars in our homes and don't have the stomach for massive military operations anymore.
Add to that the numerous laws and constitutional bans against building militaries too large (supported by America!). Austria constitutionally forced to remain neutral, Finland forced to remain neutral due to Russia, etc.
Do you really no tunderstand why Germany was discouraged and was resistant to building it's military after two fucking world wars it started?
Really?
It's not as simple as you make out. Europe also isn't one country and one law.
Someone in this thread said Americans are reticent to support Ukraine because of pointless wars in the Middle East. Well imagine how fucking reticent you'd be if a massive chunk of your population died fighting wars in your own homes and back yard?