Because it doesn’t matter.
First, middle and later stage investments (post-traction) don’t really require you to understand the technology or even the product per se. Because by then … it’s proven. However the magic dust works. Understanding the markets themselves, the investment’s market position, and being able to model the future out accurately (including multiples, price, exit timing, etc.) are more important.
Second, most B2C investments aren’t really about technology. So why does it matter? Do you know the Snapchat stack? Does it matter, as long as you can fix it later with a great VPE?
Third, you can get help. Advisors, VPs of Engineering, etc. To help you do technical due diligence.
VC is financial investing. The best VCs (1) have really strong deal flow, one way or another and (2) are really good at picking. In some cases, technical skills can help with (1) and (2). But in today’s internet world … not as often as you might expect.