I regularly conduct interviews at one of the more infamous "whiteboard interview" companies. At the end of my interviews I like to take five to ten minutes to answer whatever questions the candidate might have about myself, the company, the process, etc. One time I had a candidate who absolutely bombed the interview asked me a question that expressed a similar sentiment: why do you guys place such a heavy emphasis on basic data structures and algorithms when standard libraries and software packages offer easy to use, efficient implementations?
To be honest, this is a fair question. For someone whose entire career has been spent coding on a single machine, with data that fits in memory, reusing pre-written O(NlogN) or faster algorithms, often with a single thread, I can see why they would ask this question.
The answer is: for what we do, there is no off the shelf solution. Our datasets almost never fit on a single machine, to the point where we make jokes about five terabytes of data being so small we forgot how to count that low. Our algorithms are almost all novel: one of my favorite interview questions starts off as a trivial string manipulation problem but then branches out into easy-to-express, easy-to-understand variations that actually require some very sophisticated algorithms to solve. When it comes to pre-built software, even our internal turnkey database solutions are so sophisticated they require a solid understanding of distributed systems and operating systems to avoid common pitfalls.
Honestly, not every person is up to the task of working in this environment. Our workforce skews towards people with degrees in CS from high-ranking universities not because we're snobby but because there are few places that teach this particular combination of skillsets. You can probably go your entire career without working for us or on the sorts of problems we try to solve, and you can just as well prepare for interviews by focusing on practical matters and not deeper algorithms and data structures knowledge. And that's fine, I'm sure there are plenty of positions out there for you.
But if you do, don't come complaining to me that our interview process is too hard or the prep process is too impractical or that we're being unfair because none of the stuff we test for is practical in the real world. You can have an easy time prepping for my interview or a job at my company, but not both.
EDIT: There is something to be said for companies that cargo cult this interview process. True, if someone can pass this interview process they’re probably pretty decent, but you have to be honest with yourself what sort of problems you’ll be solving. OP, meanwhile, expressed an feeling of blanket pointlessness without saying what kind of job he’s looking for. I hope I’ve made clear this is counterproductive for companies like Facebook, Google, Microsoft, etc.