Germany is increasingly reliant on the US for its security because Germany has let its armed forces atrophy. The less capable Germany becomes, the more reliant it is on the US. It's a far cry from the Cold War where West Germany was a legitimately capable independent military power.

The US absolutely has geopolitical interests in being in Europe militarily, but as China demands more and more attention, there is increasingly less obvious benefit in the US more or less completely underwriting the defense of a state which appears keen on economically collaborating ever more closely with the US's two greatest rivals.