Earlier quoted context omitted.
I think you're misinterpreting what the post and the GP meant. What's at issue here isn't that Uber drivers don't get to take home X% of what the passenger pays, but rather that the cost Uber charges passengers isn't enough to keep the business afloat without a significant amount of VC funding.
I think the point of the comment was as kind of an upper bound. For instance if drivers made 100% (or more) of what the passenger pays, then Uber would be obviously not breaking even. At 65-75% it's feasible that at a certain scale Uber's cut would make them profitable.
1. Run their operating business - Maintain data centers - Maintain a global web infrastructure - Maintain the app
2. Run campaigns to compete in markets with strong local competition - Europe (Hailo, Car2Go, etc) - Asia (Didi, Ola, Grab, etc)
3. Finance their ongoing operations - Equity financing expensive - Debt financing hard to get at this stage and cost money too
4. Hire and retain top talent 5. Legal fees and licensing 6. Rentals for global offices 7. Fund and maintain fleet businesses 8. Invest in R&D (self-driving technology & talent) 9. Entertain M&A
So it looks they have a lot of costs on their plate which their operating business can not cover.