Earlier quoted context omitted.
It's really not that hard. I suppose there might be a few companies with insane expectations, but most interviews don't require that level of preparation.
I don't know. If all the candidates are that well prepared, then if you are not you are at a disadvantage, even if it didn't used to require it. And at companies where people want to work for, like Google/amazon/FB/Netflix, etc. and startups many people come prepared.
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.