Congratulations, you got lucky; your comment is an example of survivorship bias. You happen to have the technical know-how and people to run your own infrastructure, but this isn't the default.
Ideally you want to have multiple runners, and for them to scale so that developers aren't endlessly waiting in job queues. On top of that you might want proper network segregation, and for it to be on a separate virtual network to your workloads to reduce your blast radius. You might have problems with connecting your server to third party SaaS outside your network, etc etc etc
Virtual network is also very easy to set up with most providers (even with dedicated servers), there's pretty much zero config.
So far we didn't have any issues connecting to outside SaaS, but we host most stuff ourselves anyway, so that's not a common use case.
Why would decisionmakers want to add outsource-able ops overhead to that very full plate?