What makes you think that Germany is so special and heroic that it alone, out of every state in the world, will arrest George Bush?
It's a matter of law, not politics. Politicians don't get asked, it's all the juridical system, and no there's no legal basis to give diplomatic immunity to non-diplomats (or, to a limited degree, their direct families). You really don't get it do you. It's why Bush, unlike e.g. Obama, doesn't ever come over. He no doubt has been advised about the situation.
It's the same reason why Putin didn't come to South Africa: He was advised that he would be arrested.
it has an extremely advanced metallurgy industry,
Is that why the US industry begged Trump to cave in in that little steel trade war so that they would not have to pay premium for alloys the US industry can't produce.
it also produces 12 percent of the total microchips in the world.
Yeah try doing that without German machines, machine components, metrology equipment, and similar. The list of critical components and knowledge we or another European nation (mostly German-speaking ones though) are the sole provider of is practically endless, it's got to do with our economic structure full of hidden champions, small, even tiny, companies completely dominating the world market in their one particular and critical niche.
What do you intend to do, invade? Lose the modicum of dignity you have left on the international stage? Over a war criminal? Against the whole of NATO plus EU? Not to mention that we can sink carriers without you knowing where the torpedo came from (ask your Admirals), and the French would have no qualms to nuke one as a warning shot.
But I have no doubt that you will find some exceptionalist cope to continue believing that the US is all-powerful. That you could snip your fingers and tell us "Bush is going to hold a speech in Berlin and he's not getting arrested". That's not how the world works. The way the world works is that he's not getting arrested because he's not coming over because you'd, push come to shove, rather limit his movement than let him be arrested because you don't like where that would lead. It's the scenario everyone is way more comfortable with than any of the alternatives so it is the scenario that happens.