Knowledge is infinite. Why arbitrarily choose germ theory? Why not choose vaccines, or fertilizer, or genetic engineering, or electricity, or something so advanced even we don’t know about it?

We’re not even at a stop in history. We just coincidentally live at this moment in time.

But also, there are realistic concerns. Palestine in the first century couldn’t exactly manufacture the industrial processes required to create antibiotics for the whole world. Also,it’s not like that knowledge would reach the populace; society was very stratified at that point and an expensive treatment wouldn’t reach everyone. After all, there are communities now that don’t have access to modern medical care, for purely human faults.

Finally, saving souls was more important. Jesus’s message was that our greatest need was to be forgiven for sin. He came to give spiritual life, not to extend physical life.

Why would God not tell humanity explicitly about germ theory/antibiotics?

How many millions (billions?) in history died during childhood from something a quick round of antibiotics could have fixed? How many descendants do you think they no longer get to have? How many have starved because of pestilence which knowledge from an all-knowing God could prevent. Is it not incredibly cruel to make us figure out something as complex and tiny as bacteria? Sin may be the fault of man, but whatever version of creation you follow we did not create bacteria.