It's only after some time goes by that, as an artist, you begin to see themes emerge from the work that you do. For lack of space, walls are a good way to "store" your artwork until you can figure out who might be interested in them or who might want to buy them.
I have one last circle canvas left to paint and I'm glad that I didn't buy more. It is an unfamiliar shape to many people and I don't see any potential for sales in the future for works on this type of canvas. This is not to say that I didn't enjoy the process of working on circular canvas. It did help me to think outside the box.