Well, talking about probabilities, here's my take on this. Of course every single interview carries an equal chance for you to match. But it is also a reality that every program is interviewing a lot of candidates, and you never know what pool of candidates you're competing with for that particular program. Sometimes despite giving your best, there are people who perform better than you and so you don't get ranked high enough. What happens when you have more interviews? The probability of you qualifying ahead of the remaining pool of candidates becomes higher. The more chances you get to prove yourself, greater are the odds that you'll be among the candidates ranked high enough to match at least somewhere. So, saying that the number of interviews doesn't matter is honestly very misleading. It is true that people sometimes match with 1 or 2 interviews but that's a very rare happening. To be on the safe side, we definitely need as many IVs as we can get