Here/There you go

What does it exactly mean? When do you say it?
I know that one of its usages is in cases where you're giving something to someone.
But I hear this even in other cases where nothing is exchanged between the two people.
For example,

Bob: Why was Jill crying today?
Amy: I don't know.
Lisa: I know why. It's because his dog died today.
Amy: There you go.

It means "Now you know why." or something in this case.

"There you go" (in some contexts) means "That's the reason".

Since when did it start to be used that way? How did that come to mean what it means today?

What's the reason that people say "There you go" instead of "That's the reason" or "Now you know why"???????????????

I think "There you go" is very universal, it's an utterance of acknowledgement, and you can tint it with various emotions.

It also has other meanings. Why not google it to get the picture?

Cambridge also says:

1) I told you so
2) used to express acceptance of something unlucky

"Here you go" is totally different. It generally means that the person saying it is furnishing something to the listener, either in a real, physical sense, or metaphorically...