It's kind of absurd. These companies are trying to build a moat in an industry with very little barrier to entry and regional compartmentalization. The only thing Uber has going for it is the network effect of being available across multiple cities and countries.

How much of this "never manage to become profitable" is tricks in accounting? Would investors continue to give money after due diligence looking into the books show this constant loss and say "yes, take my money!"?

I think it's time to forgo this idea that investors do any due diligence anymore. They just look at price going up and someone hyping it going up further and jump on the train, thinking they can sell it for more later... And then justifying the price by some far future market dominance and magic tech actually coming real, see Uber and Tesla... Or even with social media companies like Twitter to actually turn decent profit...