My pet theory is that most of the investor class in seattle is ex microsoft and ex amazon. Neither microsoft nor amazon are really big splashy unicorns. Amazon's greatest innovation (aws) isn't even their original line of business and is now 'boring'. No doubt they've innovated all over their business in both little and big ways, but not splashy ways, hell every time amazon tries to splash they seem to fall on their ass more often than not (look at their various cancelled hardware lines, their game studios, etc. Alexa still chugs on, but she's not getting appreciably better to the end user over even the last 10 years).

Microsoft is the same, a generally very practical company just trying to practical company stuff.

All the guys that made their bones, vested and rested and now want to turn some of that windfall into investments likely don't have the kind of risk tolerance it takes to fund a potential unicorn. All smart people I'm sure, smart enough to negotiate big windfalls from ms/az but far less risk tollerant than a guy in SF who made their investment nestegg building some risky unicorn.