VCs aren't marks. They're fencers, hoping to get rid of the product before anyone realizes it's worthless or stolen. The (possibly sometimes subconscious) reason they don't care to deeply investigate is because if they're convinced by a shallow inspection, they're pretty sure they'll be able to convince others.
It's a greater fool shockwave, pretending to buy into something and betting that you can get someone else to buy into it before the bottom falls out. Not that you know for sure the bottom will fall out, but if you're going to buy in based on how marketable the pitch is, examining it too hard might weaken that pitch or make it fall apart. In that case you've wasted time and money and have to find something else. If you're committed, the last thing you want to do is examine the business; you're shortening your bullshit runway.
It's a greater fool shockwave, pretending to buy into something and betting that you can get someone else to buy into it before the bottom falls out. Not that you know for sure the bottom will fall out, but if you're going to buy in based on how marketable the pitch is, examining it too hard might weaken that pitch or make it fall apart. In that case you've wasted time and money and have to find something else. If you're committed, the last thing you want to do is examine the business; you're shortening your bullshit runway.