The simple yet embarassing reason why Germany is so hesitant to give military aid to Ukraine:

Hello, I'm from Germany.

The german military sucks.

Oh, Germany sells some of the best military gear in the world! For example, Germany has recently developed the world's strongest RPG: It can one-shot ANY tank currently in service in any military on planet Earth.
One-shot.
Anything.
Or Germany sells automated anti-air batteries that can take out incoming missiles and drones all by themselves.

But that's all for export.

The germany military itself gets none of the nice stuff because in Germany the military is the one part of the budget you can always cut to free up money for your political pet-projects.
In Germany, Minister of Defence is one of the least-prestigious positions in the government. There are only two kinds of people who get to be Minister of Defence in Germany:
1. seasoned old politicians with a financial attitude towards cutting spending
2. newbie politicians who are supposed to take this as a learning- and career-building-opportunity

There are two reasons for this:
1. Germany still feels bad for WWII and doesn't want to have a strong military.
2. Germany has a very strong anti-war movement. Since the 1960s. There are left-wing anti-war parties and right-wing anti-war parties in the Bundestag.



The german military itself is a cesspool of outdated equipment and absolutely embarassing administrative incompetence.

* The Marder-tanks Germany wants to send to Ukraine? They were already technologically outdated and badly maintained 20 YEARS AGO.

* The german military ordered a new assault-rifle, but the specification-sheet was badly written and it said nowhere that the rifle should be able to still fire straight after having already been fired for a while. So the heat from being fired for a few shots was already enough for the barrel to bend and to make any successive shots miss.

* The german military tried to get their own drone for long-range-strikes, the "Euro Hawk". Except whoever orered this thing on behalf of the german military got the specifications wrong, so now that thing isn't even allowed to have test-flights in german air-space because it violates german air-traffic security guidelines.

* The german navy tried to get new helicopters, except after they were delivered it turned out THAT THEY RUST WHEN EXPOSED TO SEA-WATER MIST.

* The german airforce is so under-funded that out of their whole fleet of planes, only the tiniest fraction is actually servicable on short notice.



My best guess why Germany doesn't want to send Leopard-tanks from their own stocks to Ukraine?
BECAUSE NONE OF THEM ARE FUNCTIONAL RIGHT NOW AND NEED SOME MAJOR MAINTENANCE-WORK IN A REPAIR-SHOP FIRST.