​Opinion, not fact: is it not the case that most folk who develop independently usually do so where they either a) use rbenv or b) own the machine and can `sudo` safely? And by contrast, the people who can't do that are usually in corporate environments where site-wide installation makes most sense?

Note that rbenv isn't just a workaround for this, it also allows independent installation of entire Ruby environments, including core/stdlib, parser, etc. So I don't know that we can say that there's necessarily a large number of workarounds just for local gems.