The issue is not the quality of OSS alternatives. It's that end users don't want to even think about hosting and infrastructure (leaving aside network effects for now). The same way they don't want to think about the plumbing in their home, and just call a plumber if it's not working. So I see the issue of trustworthy IT infrastructure to be conceptually similar to fatbergs, which are a mess that centralised authorities pay millions to clean up.
That's not exactly giving hope; but I would say that what makes it approachable to end users requires managed infrastructure that they don't need to think about. Including paying for it, as users have also been trained to expect to get consumer digital services for free. It's a high bar, but Signal and mastodon have some success because they provide this. DIY options like installing Linux or hosting your own service do not.