well the problem is toilets in space are a lot different from the ones on the ground. They operate on suction and with no water,more parts, smaller parts, so a mechanical part like a fan is a lot easier to break down than the porcelain gravity based toilet in your standard home here on earth. And backup parts are tricky, since they are working in an area that's smaller than a pair of bedrooms in my parents house, and its already packed full of stuff, expensive stuff. Of course, getting anything to space is expensive, so they basically just hope that nothing goes wrong for as long as possible. I mean, the damn thing has lasted 7 years, probably longer than it was designed to work for.
