If only there was some method of exchanging money for the time of professionals capable of vetting a technical product and giving a summarized report.
The outright frauds are rare enough that checking for them needs to be very cheap for it not to be more cost-effective to spend that money improving other deal-flow filtering. That's not to say that VCs aren't trying to improve on it. It's just that fraud is just one of many risks, and managing risk is about taking a dispassionate view of which measures improve your returns the most.