Are you asking why ifixit doesn't sell the parts or if the manufacturer doesn't sell the parts?
My guess is the manufacture doesn't make the parts easily available to consumers/third parties and therefore, companies like ifixit can't get a hold of them.
Manufactures have shown they love going out of their way to make access to replacement parts and repairs difficult for the sake of "safety" which really translates to more profit. Why sell you replacement parts for a few dollars when they can sell you a whole new unit for much more? From what I can find in the few minutes of web browsing is you could buy the whole motor base for about $50 US.
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