You're right that many "professional" lenses come with a flower- or petal-shaped lens hood. Such hood work better to shade unwanted light because the camera image is rectangular, not round. The hoods have deeper "petals" at the top and bottom, medium at the sides and shallowest in the corners.
However, the front of both of your lenses rotates when you focus - that means that the hood would rotate too, and would therefore be misaligned, causing black shadows along the edghes and in the corners of the image
Pro lenses tend to have non-rotating front parts, hence they don't have this problem.