It's extremely hard to make a living as an author, and it's a lot harder than it was even twenty or thirty years ago. Unless you're a literary awards darling/massive bestseller/someone they think has the potential to become a bestseller, getting a publishing deal will result in a very small advance that's not enough to live on (I've heard of authors being offered $10,000 US, which is split into three parts and paid out across multiple years). Most people who work full time as authors are either independently wealthy or have spouses with well-paying careers. Almost every other professional author has a day job (I know people who work as engineers, university lecturers, lawyers, in the public service, as librarians, etc etc — in order to make enough money to have comfortable lives, while writing in their spare time and being published professionally).