Anecdote from me: I jumped from leading an engineering team for an online virtual events company to working as a solutions engineer for a WebRTC vendor.
They asked for a reference from my previous CEO.
I had left on good terms (gave 4 weeks' notice) and was incredibly professional while working with the previous CEO, so I got a glowing reference. If I had been an ass, it'd be unlikely I'd have gotten such a great reference and got this job. ~6 months later, we even scored my previous CEO as a customer.
The tech world is SMALL. Especially if you niche down career-wise, it's possible to find yourself in a situation where only a couple hundred people worldwide have the same expertise as you. At that level, people would instead work with people they know or have strong references from people they know.