Most likely they are actually, every country will have a certain "% of GDP" threshold where once they go above that number, it makes more sense for them to spend the money in their own home grown defense industry vs buying US made weapons.
It has also certainly served US interests to keep certain European countries "down" and have them reliant on the US for their security for other reasons too.
The idea that the US decided to "subsidize" European defense for multiple decades, out of their own generosity is.... nothing short of completely laughable imo.
...biggest pushers for European nations to rely on the US, to be precise. If that's no longer the objective, fine, but there's no need to rewrite history and call it "mooching". It was a strategic choice, to avoid a repeat of WWII.
Relationships change over the course of a century. The 2% GDP defense spending agreement came about during the Riga summit in 2006. So the objective did change twenty years ago and many member nations never abided by that agreement; much to the frustration of both Bush and Obama. What you're espousing is more of a history rewrite by assuming we have had a static relationship going back to the end of WW2 and that this defense spending agreement is newer than it actually is.