I personally do it because it's challenging content. At the end of the day, this is a videogame that you play for fun.

If you're only playing because of the items you're going to get, then you might have a different philosophy when it comes to why you play videogames.

Asking what the point of doing Savage and/or Ultimate is almost the same as asking why people bother playing games like Dark Souls, or any other challenging single-player game.