The mis-use of the word Diva

According to the OED the word Diva means a highly distinguished female singer. Maria Callas being an excellent example. Now it seems to mean a woman who thinks highly of herself, has a huge sense of entitlement, can be as rude as she likes as she is a 'diva'. I've heard women refer to their brattish daughters as a 'right little diva' quite proud of the fact. Why are so many words mis-used to such an extent? Another example: we had a corner pub in my area called 'The Hogs Head' it had been there for many years. It was bought out and completely refurbished and given a new name - The Libertine. A libertine is a dissolute person - Casanova being a prime example. I asked the pub manager why had they given the pub such a horrible name. He was amazed that I thought it was a horrible name as didn't libertine mean freedom?
So it appears that quite a few people have no idea about the meanings of many words. Obviously dictionaries are a thing of the past.