Ready made curtains are very often just not long enough for the window. Add to that, in order to hang the rods, you will need at the minimum an additional 4″ of space over the window to accommodate the brackets for the rods.
Another reason is not being able to find the right colors or patterns that match the room you’re decorating. A bonus to having custom drapes made is that while you’re purchasing the fabric for the curtains, you can buy extra fabric for matching pillows, seat cushions, tableskirts, etc. to pull the room together and have a nice custom finished look to the room.
Watch this video to see more examples of Custom Drapes!