Keeping the notion of a Canvas alive (for the sake of the simpleminded among us... like me
)
Canvas comes in different grades and thread counts. Some are thicker and more durable than others, made from high quality linen thread. High quality paint or dye applied to such a canvas does not sit on the surface, but penetrates deeply into the canvas itself, and multiple layers of paint or dye must be applied to saturate and build solid colors and depth. A canvas like this may seem less bright white in appearance, but the quality is evident not only in its own texture, but in the way it accepts color.
Take a sheet of white paper instead and you have a thin, hard, fabric. Far less durable, thin, and most of the paint or dye will sit on the surface or bleed badly. It has a brighter white appearance, but it is not the same as that quality canvas you really want.