If you compare Facebook's uptime vs Reddit it is no contest. Granted, it isn't as widely used compared to Facebook Login, WhatsApp etc. but still it's impressive
One reason why this works so well is that there is often a monetary incentive on the referrer's side, in that they get paid some referral bonus if you get hired
I do not see anything less feasible doing it with threads / forks.
Asynchronous IO like in Go I think is useful in a sense that if some of the networked responders are temporarily slow then they will not hold fast ones and would not accumulate threads. If however it is disk / database, then by immediately switching to a next method this strategy will let internal async tasks piling up indefinitely and saturating resource pools of OS just as well. So those "concurrency focused" languages are not a silver bullet and one has to understand internal mechanics to properly manage requests lifecycle.