Because Vision Fund isn't this magical VC that trumps all others. They just had a lot of (Saudi) money to throw around and frankly just aren't very good at it.

Because who wants to miss out on the next Facebook!! Zuckerberg holds huge control over FB and he's a visionary. This rocket ship is going to the moon, are you strapped in?!?

TL;DR: stupidity combined with the myth of the founder

There was an NPR podcast about the guy who runs the fund recently. He’s sort of an adrenaline addict, addicted to risk