Often they owe money they can't afford to pay; some tax issue, legal penalties, child support, etc. The sov cit communities tell them what they want to hear, specifically that they can get out of their financial obligations without paying by using esoteric loopholes. There are authors, podcasters, YouTubers, etc who profit from this sort of grift, but the sov cit movement has hit critical mass and now a lot of idiots are just feeding off of each other's ignorance for free.

It's incredibly easy to convince people of something they desperately want to be true. Same reason there's always a new "get rich quick" and "lose weight without changing your diet/exercise" scam going around.