Why make up a word combining two words when one of the two words does the job just fine??

Been busy lately? Been up to much?

Or have you just been chillaxing?

There's a word I don't understand. Well, I do understand it, but I don't understand why people use it.

It's a combination of Chilling, and relaxing, which means erm, relaxing.

So why combine two words to make a word that does not exist, when one of the words you're bastardising works just as well on it's own?

Insania.