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.