Well, nobody NEEDS a website. It's just a preferable method of making money through passive income on the internet.
See, if you have your own website, it means that you have your own means of creating a profit. Generally, most people would turn this website into a blog in a niche - if you like traveling, you would probably create a travel blog. That would be your niche. Then, they would start creating posts, maybe posting once a day, or once or twice a week. After a period of time, they start to generate a large following on social media, and have a large audience interacting with the blog.
This is when creators employ affiliate programs like Google Adsense, which place ads on your website. You get money based on how many views/clicks the ad gets. The more people in your audience and on your blog, the more money you make!