I think that they are working to bring up all of it, but it is taking quite a while. The nearby share feature seems the be specifically for people who live in places with either poor internet or under oppressive regimes. With it, all you need is one person to get a copy of a communication app like Briar, and then they can immediately share it out to lots of people directly through F-Droid. F-Droid isn't there just to be a FOSS app store, but it also seems to specifically serve as a source of apps for people who can't get these apps safely. This also explains the high focus on legacy support.