You are suffering from survivorship bias here. Most companies don't make it through such trying times, but those you cite succeeded against the odds to become these seemingly unstoppable behemoths.
It is true that all these high-growth companies go through major adversity on their way to the top, but this is where most end up failing. Just like every other high-growth company, Snap's valuation is predicated on atypical future results.
Even without adversity they have a tough road ahead. I would posit that there's a good chance the executive team & investors saw the writing on the wall and took the company public to get out before it totally collapsed.
It was a pretty strong signal that Evan & Bobby are primarily money-driven when they took $10M each off the table during the B round. Other notable companies where founders have done this sort of thing have resulted in fast spike-and-collapse results: Foursquare, Zynga, and Groupon.
Zuck didn't take an early multi-million dollar cash-out. The Instagram founders didn't either -- they were living in 1-bedroom apartments a year after the acquisition. Founders who believe in the long-term success of a company don't tend to get rich off a company that has not yet attained either their vision or produce significant wealth for itself. Obviously causation != correlation, but this is a pretty strong signal about the motivations of the founding team.
It's certainly their prerogative to cash out early. I'm not making a moral judgement here. However, as a value investor this is a useful signal for high-growth tech companies. This all sounds incredibly cliche, but I just don't see signals that lead me to believe Evan & Bobby have motivations in the same category as Bezos or Zuck or Jobs. All the signals are that they appear to be looking to get rich to live a life of luxury, not build their life around their company. As a human, I personally would prefer the former. As an investor and employee, I want to put my money and time into companies lead by the later.
[Disclosure: Former Instagram & Facebook employee. I don't currently own any Facebook shares]