Yeah I get that it's after market and everyone says they are junk. I'm just curious as to why. Is the metal cheaper or is the torque lower than the oem?
Well... the why is the busted in half shaft.
It's really everything. We've seen a bunch break like the one in your pic. We've seen the windings throw. We've seen the magnets crack (and grabs the arm) we've seen the copper plates on the comm delaminate. And so on.
Basically... they are Chinese. The company's who produce them can only COPY products, and don't understand the product. and they are just poor quality. The OEM, Japanese starters are ENGINEERED by a company who has been making starters for a VERY long time, and know what they are doing. AND, supply starters to dang near all the big OEM's out there. (Toyota, Honda, SeaDoo/SkiDoo/Evenrude/BRP, Polaris, Suzuki, Kawasaki, Hyundai, Kia, Kubota, Chevy, Dodge, and so on...) FYI, the OEM is Nippon Denso.
The OEM starters are so well built... I can generally take a 20 year old OEM... take it apart... buff the Comm... clean out all the old carbon dust... replace the brushes... and they work good as new. (FYI, you can use the import brush kit. they are fine in an OEM starter)