I think it was Ben Horowitz, in his startlingly self-fellating high-fivin'-white-guy autobiography, who observed that venture capital funds anticipate a payoff from one in a hundred investments, and that they expect that one in a hundred to more than make up for the rest.
Which gives lie to your imperative: there's nothing saying you must have the monetization functionality incorporated from the beginning. After all, Google didn't and look where that got them. And besides - Jerry Yang at Yahoo didn't have the vision to imagine the monetization which is why they didn't buy Google for a million dollars backintheday! Cautionary tale! Cautionary tale!
So what you get is this bottomless sea of money sniffing around going "is there slightly better than one in a hundred odds of you making my money back someday, somehow, don't care?" and rewarding preposterous bullshit like Juicero with $120m in funding.
...and having written that, let's take a step back: A company selling juice, with a supply chain, physical product and stuff people actually had to pay for got $50m more than Yik Yak. And it was a semi-absurd product, and they didn't really think things through, but Yik Yak had a fucking app. THAT'S IT.
And I look at this, and I think about the swarthy Russian doctor who came to my house to draw my blood and take my blood pressure as part of the physical I needed to get the life insurance the bank required so that they would loan me $350k for a fuckin' brick'n'mortar buildout that they're guaranteed a 4% yearly return on and I wonder how much better the world would be if guys like cgod and me could tell a VC fund "yeah, we think the odds of this not crashing and burning and blowing up all your money is a little better than 1%" and be fucking showered in money while assholes that want $73m to stake an anonymous hate messenger would have to stake their fucking blood in it and sweet jesus, I really want airborne rabies to break out in Silicon Valley.