Via Avclub.com:

Most people—at least those who are relatively nerdy—will remember Max Rebo as the blue elephant keyboardist in Jabba The Hutt’s band in Return Of The Jedi. He’s probably one of the sillier-looking Star Wars aliens, but he’s not quite as bizarre as some of the creatures that would pop up in future movies. If the production had stuck with Max Rebo’s original design, though, he could’ve easily been one of the weirdest aliens in Star Wars history. A post on the Star Wars website called “Getting To The Bottom Of Max Rebo” dug into this a few years ago, and it explains how the character’s original design didn’t have any arms. That may seem like a bad choice for an alien keyboardist, but this incarnation of Max Rebo actually sat on a cushion and played the keyboard with his feet.

The limbs on the finished suit in the movie ended up looking more like arms, so that’s what people assumed they were (as seen above). So, when Kenner made the first Max Rebo toy in 1984, he had arms and legs. Since then, that’s been the established look for Max Rebo and any other Orotlans who pop up the Star Wars universe.