> Is this just a really well kept secret

It's very hard. Not having FANG/unicorns on your resume probably contributes massively to this. FANG style interviews are a skill of their own - I recently had a 6 hours of interviews back to back with Amazon and it was a mix of pretty tough technical questions and very specific behavioral questions. Even with practice solving sole of the question was very hard. For instance, I solved a DP question in a top down and interviewer asked me to then solve it bottom up for him in the remaining 5 minutes. You can't do this without a solid amount of practice.