Because it works.
They wouldn’t do it otherwise.
Facebook, Pinterest, and many other top B2C deals were sourced this way.
In the B2B world, well yesterday, I was intro’d by a Top VC who wrote a term sheet at $12m pre for a pre-revenue start-up an associate brought in via cold outreach.
Partners end up being in-bound folks, mostly. They source from their networks, their referrals. And their associates.