Shooting on the street is fun, challenging, enables you to get technically more competent, allows you to try various techniques, allows you to interact or ignore what is going on, allows you to shoot a huge variety of things (streets are all very different for example), and it focusses on the thing that the vast majority of people find interesting in a picture, other people.
Personally I find landscapes very dull, but I understand why other people like them and also appreciate what goes in to making a good one. I don't argue the toss about it though. I like shooting on the street, I find people interesting, and I love the challenge of shooting somebody whilst they and I are both walking in opposing directions, giving me almost no time to get it right. When I do, I am a very happy bunny.
That's my simple argument for why I like street. 🙂