I think the reason it keeps going is that communities get more extreme over time.

I remember seeing an explanation for this a while ago, and don't remember the full details. The explanation went something like: say a group starts getting more extreme. A less extreme member might see that and drift away from the group. There are probably plenty of groups they can join that are less extreme. OTOH, imagine a group starts drifting towards the center. People with more extreme views might not have a more extreme group they can join, so they stay and fight the change. Because the people with extreme views are the ones who don't drift away, the group tends to get more extreme over time.

I would bet that with Sovereign Citizens, the people who have doubts are pushed out. If someone says "this didn't work", other people will say they didn't do it right, or that they're lying, or that they're an agent of the deep state who is trying to discredit them. The extremist people who are sure it works are the ones who stick around.

So, even if 99% of the time it doesn't work, the SovCit keeps going because the extremist people stick with the group, and new members join over time, while the less extreme members drift away, including those who discover it's all BS.