Ever return to a reunion and been frustrated when former classmates are surprised at your success? It may be human nature to pigeonhole each other, and since (most) clients are human, they have a natural tendency to make assumptions about your abilities that will be tough to change.
Smaller ships turn quicker, and your capabilities are likely to expand more rapidly than client needs will evolve. You are a smaller firm than your client, and are likely adding capabilities very quickly. That’s another way of saying that clients may have you in a rut.