Sorry I was trying to be pithy :)
jkimmel explained what beta is. The Tech industry as a whole has a high beta, and the smaller loss making component (i.e unicorns) an even higher beta. I am using the term beta loosely here as most of the unicorns are not public so they don’t really have a true beta, but they do have a pseudo-beta. They are being funded by private equity funds in what are effectively private IPOs.
The problem is that private equity funds are a high beta asset class. In times of risk aversion investors pull their money out of high risk asset classes and put them into lower risk asset classes like large public companies and bonds. Relatively small changes in investor preferences can get amplified up the investment chain resulting in large swings in demand at the far end.
A hypothetical example might be 10% of investors pull their money out of private equity funds, the funds find that most of their money is locked up in illiquid assets like loss making high growth tech companies (i.e. unicorns). In order to return the 10% of capital requested they have to cut new investments by 50%. The unicorns find that they are not able to raise the money they need to expand at the pace they have been and so go on a crash program to achieving profitability. They lay off developers, cut back on outside services, and stop buying small start-ups. VCs and angel investors seeing this cut back on investing stop putting money into new firms further decreasing demand. All of this is not good if you are running (or wanting to start) a business based on rapid growth that needs lots of capital.