In the world of traditional publishing, there’s a certain order of how you get published. First you search for a literary agent. Maybe you spend weeks and months gathering a list of potential agents. You create the perfect query letter and send out. Then… you wait. If you’re lucky you’ll get an agent and possibly a publishing house. But if you’re lacking a platform, you may not be able to find an agent who’s willing to take you on.
A platform is you’re selling point, it’s what entices agents and editors to take the risk of publishing you because they think you’ll sell. Generally speaking if you’ve had previous publishing credits to your name, such as a magazine article, you can use that as your platform. If you have a million followers on your blog, that’s a platform. If you’re a celebrity or a politician that is a platform. The reason most traditional publishing houses take on celebrities and politicians is because they will sell. It’s not a risk for them and in this day in age, publishers aren’t really big on risks. It can cost a lot of money to publish a book, between cover artists, the book designers fees, editors, ISBN, and stocking fees for the psychical stores, a single book can run in the tens of thousands for a traditional publisher, and if they can’t ensure you’re going to make back that money that they invest into you they don’t want to take the risk.
People will buy books from celebrities because they know them. They trust their opinions (for the most part) and that’s why publishers are more willing to take them on. It could be argued that people have a harder time trusting new authors, and understandably so. For every Harry Potter, which I’m sure most would like to believe they are, there are plenty of books that will rarely see the light of day.