Why aren't MBB (and other firms) upfront about the amount and type of of preparation required to be successful at interview?

A number of comments here:

1) Firms underplay it because they don't want candidates that will be good at interviews as a result of countless hours of practice - they want candidates that demonstrate the key skills/qualities that consulting firms look for. To demonstrate the core of these, 5-10 hours of proper practice was typically seen as enough. Firms don't want to miss out on potential strong candidates just because they were not aware about consulting 6 months before interviewing and could dedicate countless hours to prep - so major firms at target schools often have case-workshops to try and limit this bias.

2) In a way, it is due to sites like Victor Cheng and PrepLounge that has led to the requirement for most people to do many more hours of practice. As everyone has access to more and better material, the average quality of interviews increases - so firms have to be more selective, and the "passing criteria" have become more and more demanding.

3) Finally, on your point about DCF - I think this is a huge misconception. If you are applying from undergrad or from a non-business background, you will not be expected to understand DCF, NPV, etc. Part of the reason people think this is expected is because most case resources come from business school (MBA) case books - where students learn these topics, and see firms might choose to test them on their knowledge. However, I can guarantee that if you are applying to MBB out of undergrad, you will never be expected to know these technical terms/methods, or be penalised for not knowing them. The only exception might be if you are applying to a very specific role within a company (e.g. M&A advisory) where e.g. NPV might be particularly important.

Hope this clarifies some of your questions.

Honest answer: Because if you're not able to find that out on your own, you're probably not cut out to be a successful consultant.

That being said, I don't believe it is necessary to do 20+ hours of live cases to pass such an interview. Even MBB only cook with water, and too much preparation can also lead to "analysis paralysis". There are definitely diminishing returns, maybe even negative returns to prepping too much.

You easily come across as a robot that memorized everything, rather than an authentic, intelligent human being. I personally always prefer a candidate who is able to think on his or her feet, can creatively tackle problems and who has the openness and backbone to admit when they don't have a clue over someone who has memorized 327 frameworks and 713 brain teasers but is about as relaxed and authentic as Cher's face these days...

To me, talent, raw intelligence, creativity, and personality beat preparation 10 times out of 10 (I mean as long as it's not evident that the candidate just is sloppy and doesn't give a f*ck). Facts and methods can be taught, those qualities can't.

(edited)