If you forget to autoclave them or not done properly you end up with infected patients, risk is just too much

We sterilize plenty of other common tools like scalpels so that doesn't seem like a valid reason. Obviously the disposable design is not even an adequate solution to the risk of cross contamination. I would imagine if it were a real concern you could easily add something like a color changing strip that would indicate whether the needle has been autoclaved since its last use without rendering it useless.

Sounds like the same risk as this situation of reusing them.

Prions aren't destroyed by autoclave