Why Rudolf Carnap decided to change his opinion on verificability principle?

Can anyone explain to me, like I have four years old, why Rudolf Carnap, an analitic philosopher decided to give up on verificability principle? If I understood it right, which I'm not sure, the verificability principle states that a sentence or a word must have an empirical correspondence and to have tautology. In other words, when I say say, this word must be connected to something physical, which it is.

But, what are the reason for giving up on this principle? I heard that he switches to the tolerance principle, which states that there are more true logical language structure than one. He clasifies those languages into 2 (e.g. Language 1 and Language 2). From my poor understanding, the first language is simpler and the second one is more complex, which is used in scientific theories (e.g. Relativity Theory).

So, I would like to know why he give up on the verificability principle.