> I’m saying that services that are like GitHub are ubiquitous because they save time

Popular services are ubiquitous for many reasons, some of them based on actual value, some of them based on perceived value, and others based on things orthogonal to day-to-day value like organisational inertia, aspects of network effects, etc. They may save time for you. Others may have chosen the service for different reasons: either wise or ill-advised.

> easily 5hrs a week

Subjective. But also, more importantly, subject to error based on your metrics. How have you quantified time saved by Github?

> creating them anew would cost more than those services do if you buy them as a user (gitlab enterprise or github “pro”)

This is, I think, where you're missing my point. Of course creating them anew would cost more than those services do. That's not the question being asked here though. What's being discussed is whether using Github will save you time over not-using Github.

Not using Github does not necessarily mean maintaining an equivalent service itself, because that presupposes that the features provided by Github save you time as is. The only reason you would host an equivalent service yourself is if they definitely do, which isn't a certainty.