Counting Words

I've been working on a new novel a little bit at a time and have over 15,000 words. I've never been one to keep up with word counts but I wonder why do we as writers have to have a certain amount of words? I'm hoping to get over 50,000 words on this novel but I doubt that will happen. I can sometimes get my ideas and thoughts across in half that amount. I doubt I'm the only one. I fear that people who write articles and novels and get paid by the word will put in information that is unnecessary just so they can get a few extra dollars. While I understand that it also feels wrong. Some may even make up the information and tell lies just so they have at least them minimum amount that their employer wants. So I won't worry about my own word count and just hope that you all enjoy the stories that I write.