You can write one good book, and it's fine. Sure, people may ask you to write another, and one book is not a career as a writer, but if the book is good it can stand on its own and be read and enjoyed and learned from for decades.

You need to write one blog post a week, minimum. Three a week, daily even. For years and decades. If you don't regularly publish a new post, your blog withers, and if you stop entirely, your blog dies.

It's hard to have that many new things to say, let alone things of value.