"It usually takes at least 5 years to build a company to exit or profitability."
Five years is also roughly the time frame of Venture Capital funding. With Silicon Valley companies, it
may be a bit of the tail wagging the dog because exits are often driven by investor timelines.
Or it could be, that over time, funds worked out that the time taken to build a business to sustainability took about 5 years and designed their fund lengths around this.
I would say it's far more likely that the funds followed pre-established patterns than they created the patterns.
Five years is also roughly the time frame of Venture Capital funding. With Silicon Valley companies, it may be a bit of the tail wagging the dog because exits are often driven by investor timelines.