It's called a colloquialism or just "vernacular". It just sounds pleasing and is a different way to say something. Humans tend to like variety, that's why we have so many words with so many different synonyms (some do have varying connotations, some exist to distinguish between levels of speech/class, and some are just up to preference). Language is a living thing. It evolves. You can hate that it does or you can learn to appreciate it. It's a fascinating study if you've the patience and passion for it. Teaches you a lot about how people think, how they interface and interact with the world.
