"...but there are hundreds if not thousands more startups that will make their founders and investors rich."

I think the correct word here would be "richer". For VCs 5x return on an investment while desirable, it's not the ideal outcome.

Consider a VC invests in 100 companies during X years, $1 million each. Ballparking here but 80 of these will be a total failure. 19 of them will make 5x return. That is -$100 million spent and $95 million gained. So if the last one is "only" a 5x return the VC gets their money back (-inflation, time spent, etc). Thats why they are looking mostly for Ubers and AirBnbs imho