That part i understood but again why the pushback?

The German pushback stems imho from Merz belonging to the CDU, whose political core can be summed up as

• Almost completely blind worship of the USA and
• Class warfare against the working class.

In their mind they just need to wait out the Orange Man and then most things can just go back to how they were before. They don't want to make Him angry in the meantime, which the "associate member" label would certainly lead to.

EDIT: Ursula von der Leyen is imho actually pretty far removed from her party's stance on this.