It often starts with some form of financial trouble, and not being educated in how money, the law, or any of that stuff works.

So you sign a piece of paper saying you get a truck, and they get $350 a month. This sounds great, so you don't look any further since you don't have the best work history, but right now you can afford that usually.

Later, your money situation is worse and you miss a few payments. Suddenly, they're sending you this letter that says they're going to take your truck.
It's bullshit, they can't take your truck, it's yours. You never agreed to let them take it, you just owe them something like ten or twenty missed payments.

So you start looking around for what you're supposed to do with the letter, and most places say "pay your bills" or "nothing can be done at this point", but it's not fair that you're loosing your truck just because you're not giving them money fast enough, and you need your truck.
But, you find some people who explain that there's actually some holes in the law, and point you to the law so you can see for yourself. Finally, someone is actually explaining something helpful!
If rich people can use loopholes to get out of stuff, why can't you? The only difference is that they have people who know the law, and you just found some people who will explain it.
The law says that if they can't prove that you owe it, then you don't. The people explain that you need to ask very specifically otherwise they'll be allowed to ignore you. They reference you to another forum where people have more details, and a lot of other stuff you never even thought about...

Anyway, since you had once acknowledged that you bought the truck instead of possessed it, they were able to get out of the loophole and they stole your truck.
That's okay though, since you've been reading and now you know that the law doesn't say you have to pay with money, but you can also pay with a "promissory notes", which someone sold you the template for making, so now you can buy a new truck, agree to whatever terms they want, and use your notes to direct them to collect the money from the taxes you pay. It's great because you get your truck and keep your money, the dealer gets paid just not how they expected, and the people who make up money (turns out it's not real? They just stole all the gold‽) send their fake paper to whoever.
The system is perfect, but complicated, so you'll inevitably make mistakes and face consequences for them, but if you just keep learning the loopholes and getting the special plates and drivers licenses you'll be okay.

It's a coping mechanism for people who are faced with an overwhelmingly complicated social system and don't have the tools or capacity to learn how to interact with it on its terms.
Most people in that situation don't fall off the ledge, but a handful of them are confronted with how overwhelmed they are at the same time they're offered a hand hold to something that feels like control.

There doesn't always have to be a crisis, sometimes they just see the handhold and grab on, but usually their story ends up having some routine legal or financial trouble.

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.

How do you fall down such a rabbit hole that you believe this dumb shit??

To paraphrase George Carlin:

Think for a minute how dumb the average person is...and then realise that half the population is dumber than that.

The wet ink contract. Hilarious.

I mean, how different is it to believe in some sort of invisible being that requires you to worship it in order for your soul to be put in a good place after you die?

People want existence to be more than it is and they think that if they wish hard enough it can become true. They want an easy answer.

lOl nothing every works for them