If people at Google were interviewed by juggling raquetballs, there would be books, courses, etc. on how to juggle better. People are willing to pay for this prep because they want to work at Google. Eventually most everyone interviewing at Google would be very well prepared to juggle.
Obviously if the process was a 100% fair assessment of knowledge and potential and people do better than you then good for them.
As someone who gives a lot of interviews, I'd love a better way to assess a candidates ability that is less gameable, but we haven't found one yet.
Other companies are much more specific in their interviews...you actually get a specific JD with expected skills that you hope will form the basis of your interview, and not all JDs require you to be a distributed systems/algorithm wiz.
This is exactly the concept of an IQ test, right down to the stack ranking.
They're pretty well understood by now, and they take less than a day, which compares pretty favorably to "months".