Will 10,000 followers get you a book deal?

I have heard versions of this from many writers over the years:

"An agent told me that if I had 10,000 followers, they would sign me."

or

"The publisher is interested, but wants to see 10,000 followers before they commit."

In every case, the writer was clear that the primary interest of the agent or publisher was that they truly liked and wanted to represen…