The biggest factor, in my opinion of course, is that some large private investors realized that they could capture most of the upside in an IPO before the IPO actually happened. The first real example of this is DST and Facebook. This has obvious advantages for the private investor -- they get access to a source of high quality risk for their portfolio. It also has obvious advantages for the company -- they get access to capital without having to manage to Wall St's expectations (and that's no minor thing).
Facebook was sort of the proto-unicorn, and it spawned imitators. Those imitators were not just startups, it also spawned imitators on the investment side. Suddenly a source of relatively easy money -- the initial IPO allocation in "sure thing" companies -- weren't available to the usual suspects, and those funds have naturally followed the leaders into the D, E, and F rounds of the new breed of unicorns. These deals are even accessible to relative small fry now -- private bankers will routinely shop around access to these funding rounds to people with assets "only" in the 10's of millions. Sometimes they're shopping a theoretical deal that they want to present to the company in question, and sometimes they're shopping AirBnB.
At any rate, many of the gains you used to be able to get in companies like Amazon or Google are now going to people able to get access to these pre-IPO deals. Financing private companies is very different now than it was 5 years ago.
Unicorns and Valuations are like Schrödinger's cat... until you open the box they are neither dead or alive, not worth 10Billion or Zer0
The overhead, requirements and legalities are there for a reason. If you've raised $10b, you can afford the overhead dollar amount; but can you afford the visibility?
It's very hard for a tech company to thrive in that kind of environment - capital expenditures required to develop new products or enter new markets will often not be profitable for several years, and getting the public market to understand that is impossible.
I mean, is there some kind of truth that it's harder for public companies to do ultra-long-range moonshot stuff? Maybe. But the idea that this is what's keeping Uber or AirBnB or Palantir from going public is ridiculous.
When private funding is available, IPO is not needed by definition. And since comp structures are set up with the expectation of IPO or exit, it's employees who are affected.
If you are negotiating an offer with a private company, you should attempt to price the risk of having to forfeit your stock comp. This risk has increased recently (that's what this story is about) but most people still under-negotiate it in their offers.