I heard this quite often. A writer defining his market as enormous with hundreds of thousands of people hungry for his words. Science fiction, romance, crime, and so on. First image that come to mind is that writer in boat looking at me standing on the shore while he happily paddles himself towards the horizon.
There is no starting or ending point. No island to stop for a break. Just water and more water. The food provisions will run out soon.
A self-publishing / writer is like the small boat. Lost.
A publishing house is like a ship. It has all it needs to conquer the huge market in the horizon.
Be smart. It’s not sexy to start small, but it’s the best place to start.