It's worth noting that most of the open source software that self hosts becomes an ad page or malware site within a few years once it's abandoned. One advantage to hosting on a shared site is that the project can live on. Or, at least, the binaries and source are still available for interested parties years after the developers moved on, lost interest, or passed away.
A site like Github that hosts open source projects brings a lot of value to the community. Great search, and the same UI when going from project to project. This would be much more cumbersome and time consuming if every project was on a different site with a different interface.
Also, many open source projects don't have the money to afford bandwidth costs of providing large software downloads.
I'm not saying GitHub doesn't help. SourceForge did help at time. But if you value your freedom, you need to understand that, if you don't have the keys of your infrastructure, you are locked to the good will of the provider (and its stakeholders).
I don't buy the money argument. If you have the chance to be a successful enough open source project, you will find hosting companies ready to help you with free VMs.
If you are not that successful, you can use github & co without fear, nobody will try to insert crapware in your packages. And if you want to selfhost, even a raspberry pi will have enough power to serve your site.
I think the point here is "reasonably popular", which project would you place here ?
The costs are directly proportional to the traffic but nowadays most "reasonable popular" open source projects can get hardware (VMs) from hosting companies for free.