I think the difference between source repos and arbitrary data objects (which are as often as not images or videos) is that people tend to mirror repos locally indefinitely, especially if it's a local cache of something that they're repeatedly using as a dependency for other software that they develop.
If anything is good for the bittorrent model, it's git/source control. Movies and images get moved to different drives or deleted, movies become far less worthy of keeping after being watched, and images may have never been useful to the person mirroring them anyway; just a favor they were doing for a site they like. Source code sits, and source code continues to be used. If I understand correctly, Radicle works as your local git server, too.
The question is whether people will dedicate a little bit of bandwidth to seeding, but I don't think it's a serious question. It's a cheap and easy thing to do if you want to help FOSS, and it's obviously a good and a nice thing to do. It's not like you're seeding stuff that you don't know what it is, or why it is useful.
And, again, they can keep a seed up indefinitely. But they don't need to have either great uptime or great bandwidth.