It’s a question set up to get an honest answer. This opens you up more, so you’re not answering like a robot, so they can get a better feel for who you are. You’re supposed to build on that question with more drill down questions.
The easy answer is: “I think this job will be a good fit for me and I will be a good fit for this job.”
“Why?”
“I’m a good driver. I’m a good communicator. Etc.”
“I want to work at McDonald’s because I like the food. I eat McDonald’s a lot and would be happy serving it to people. I want to work in fast food because I like working with people and helping people.”
“I want to work as a pizza delivery driver because I like driving. I have my songs on mp3 in my car and my time driving is fun. While I am happy to deliver pizza with a smile, I prefer to work alone instead of at a busy store. I chose pizza hut because it is my favorite pizza.”
“I want to work at Old Navy because I like shopping, clothes, and old navy. It matches my style and I know I can help others find the right old navy clothes for them. I like helping people, especially giving them clothing advice.”
It’s to weed out people that don’t have the social skills to bullshit through an interview.
That’s the reason for alot of interview questions in general. If your job involves people they want you to be able to have the right answers for those people.
If you have a hundred people who all could probably do the job well, you need some way to differentiate them. Might as well pick the most enthusiastic fool you can find.