YC is playing a numbers game. Their whole play is to give money to those N founders who they think have the highest probability that their idea could become a very big business and very quickly. They also know that they will have may be handful of “winners” and that even the most promising founders and their ideas are most likely to fail. So to ensure that they really only pick the most promising ones based on what they can see/tell today, they are ruthless about anything less than ones that look extremely promising. In a way they are looking for extreme and obvious standouts. To borrow an analogy they are looking at the waveform and identifying the spikes. As that’s the best they can do(regardless of if they admit to it or not). That why it’s a numbers game. And 10 minutes is plenty for that.
If anything, if they spend more than ten minutes they not only lose on the numbers game as their “pool” size becomes smaller but also diving into more details will add more noise to the signal and will work against them. they just want extreme standouts from the get go and not the standouts they rationalize after a big deep dive. The deeper the dive the more they risk their biases affecting them.
Finally this is not their first rodeo - imagine if you have interviewed hundreds or thousands of founders to evaluate their ideas. You’d have a decent understanding of what a “spike” looks like on a waveform.
Would (genuinely) love to hear a counterpoint