A decentralized alternative Lemmy[1] is already quite feature complete and in many ways even better than reddit itself. It's just a bit of a ghost town and many of the instances are aimed towards and/or controlled by political/social rejects.
"just"? Reddit is the community, not code. Users aren't going to run off to Lemmy or any other site. It just isn't going to happen.
The alternative site (and it has to be one site, nor multiple, topic-specific sites) has to either already be massively active when the triggering event occurs.
Also, once you're logged into Reddit, the friction of exploring a new subreddit is essentially zero. Compare this with needing to sign up and email verify etc every time you want to join some random phpBB forum.
My design skills (rather lack of it) is to blame. Apologies and huge thanks for the feedback. I will improve it this week.
With each passing day, the Internet looks more and more dire.