Artists are always looking for ways to make a living. One way they can earn money is by accepting commissions, providing unique one-of-a-kind items to customers who want them.
Other clients may not be able to afford the piece that best meets their needs, so they'll request a scaled-down or cheaper version of it, which is then modified to suit those requirements.
For example, a client may request that you change the artwork's color. An interior designer might redesign an artwork to fit within the project's color scheme, while a corporate client may want their logo or similar imagery on the piece.