There's this process in language where intensifiers

words that amplify the strength of the meaning of the rest of the phrase

tend to become used in areas that they aren't really truly appropriate in and thus "weaken" in meaning.

So, for example, "awesome" once truly meant "awe-inspiring", but it's been used enough in weaker senses the past several decades here in California that it doesn't really mean that any more. It just means "very good" now.

I don't think that the Brits do that with "awesome"

or at least not as much

but they like to use "colossally" in a similar way.

The above Wikipedia link has a list of intensifiers, including "literally", and you can probably recognize a bunch of them that have "weakened".

As I said in another comment, it isn't just using it incorrectly that's annoying, it's also using it unnecessarily. People use "literally" for emphasis in sentences where no adverb is needed. It should only be used if you are clarifying that you mean literally when the sentence could otherwise be interpreted as figurative