I think when people say buttercream cake, they think of very dated styles of decorating. Big buttercream roses, shell borders, etc etc. When someone (like yourself) is very good at using buttercream, people probably assume it's fondant. There are amazing (and professional!) things that can be done with buttercream by those that are very skilled. Perhaps some of cake world just needs a lesson in what really is possible with buttercream!
As a side note, most of my cakes are requested with my home made MMF fondant. I've found fondant, at least MMF, tastes very different when freshly made. Even 24 hours after being made it has lost some of the flavor and the texture changes, but the fondant I use to cover my cakes is usually made right before I put it on, or not more than a few hours before I put it on. I know most people let their fondant rest, and I wonder how much that affects what people think of it when they eat it.
I am always trying to convince customers to go with a buttercream design. I've actually considered running a promotion to discount buttercream ruffle or petal style cakes so I can do a few of those!