There is an assumption that published authors have an easy time writing books. Not true.
Writers do need to write though.
They may systemize parts of the series of books they write. They may have techniques to keep them writing. They may use assistants to help organize or assist them virtually.
Writing is hard because almost no writers will ever write once and publish exactly what they wrote.
Editing and rewriting can seemingly take forever.
Here are a few known writers who wrote about the struggle of writing and how to overcome these struggles: