So how is your interview process better than theirs, since you keep getting these lousy people? I saw many worthless people in the places I worked at before Google, then at Google I didn't see anyone close to that bad, so to me their process seems to work. They were very open about their data around hiring and scoring hires as well, and that data was very clear that the interview they arrived at was the best interview, they tried and experimented a lot and arrived at it.

Alternatively maybe those people were just unmotivated to work for you and spent their internship preparing for Google.