Germany blocks any 2% fixed target because our current government is enforcing a zero-debt budget (surplus, actually, due to higher-than-expected tax intake).
Well, that and our military wouldn't know what to do with an extra well over 20 billion Euro per year. That's three times the current procurement/investment component of the German defense budget.
Aaah, but some other militaries could use it.
Germany could, for example, finance a lot of joint EU-cum-NATO Europe support assets: a tanker fleet, transport ships & aircraft, & ISR. The need for this stuff has been shown, with the US having to supply it to support European countries. It shouldn't cost $20 bn a year, but it'd take a goodly slice of it.
It could start by buying out the Russian interest in two Mistral-class LHDs. They're ideal for floating HQs, are equipped to carry hospitals, can do disaster relief, transport - all sorts of stuff, even if nobody on board ever fires a shot.
Throw in a bunch of militarised ro-ro ships (Flensburger has an excellent, well-proven, design) in place of the leased ro-ros - & a few more of them, enough A330 MRTT so that European countries don't need to piggy-back off the USAF, & all the A400M that Germany thinks are surplus to requirements (perhaps reinstating some of the cancelled ones & buying some more AAR kits), & just about everything except underway replenishment of naval ships would be sorted, And why couldn't Germany provide some of that?
Then we get to ISR: the NATO AGS has stumbled on from cut-back to cut-back. SIGINT is a gaping hole, despite there being a perfectly good sensor package (paid for by Germany) available, sized to fit in a big UAV but which could fit on a manned aircraft, e.g. a long-range bizjet. If if really isn't practical to fix EuroHawk, then bite the bullet & find an alternative platform - & more of 'em. And while you're at it, sort out a European alternative to all those Reapers, Herons & the like out there, for a pooled capability. Doesn't have to be German: there are non-German platforms ready & waiting for a bit of investment & an order.
Satellite comms & surveillance - oh, so much that could be done!