Sorry for coming late but I don't think any of these posts address your question or even understand your confusion.
If were looking for a proximate or direct cause: There are so many places where, if Jonas intervened (supposing that intervention is possible) with the anytime-dark matter machine, it would have prevented the successful creation of the chair, which would have prevented Erik Obendorf from getting kidnapped, which means the kids would not go to the caves. Shit he could've just gone back to the caves before they all went in and said - go away. That would freak them out.
On the other hand, if we're happy with just a "butterfly flaps its wings" distant cause that would've just changed how pretty much everything turned out, then pretty much any distant cause would work. Slashing the tires of one of these people's cars in 1953 would've changed every single thing that happened afterward.
The problem with too distant of a cause is, well, first, it's not dramatically interesting. But the real reason there are restrictions on the cause is that the choice of when to intervene is constrained by at least one condition: that Martha is born and lives. So he can't just go back and kill hitler as a baby. Which would be a really big butterfly effect. Martha wouldn't even have been born.
Now it's immaterial whether Adam is just lying to Jonas about his ability to intervene; the choice of when is supposed to make sense to Jonas (otherwise he'd respond, wait, why don' t I just go kill young Adam? Like right now? I know you've got a gun around this place so give it to me, and I'll go right now and this whole thing can be over. If I kill young Adam then there is no chair, no Kidnapping, no cave-stash search.)
So why doesn't he just kill Adam? Or just cut the line any where before the first kid goes missing in 2019? I think the answer is there is actually another constraint at play: he wants to not be erased from history in the process. He wants to intervene in a way that will make it so things go back to normal, the way they were just before his father killed himself.
If we take this as his goal, then the REAL question is whether he is trying to prevent Mikkel from being kidnapped in the first place. If Mikkel is never kidnapped, Jonas is never born. And we know that not only has Jonas had the chance to return with Mikkel in season 1 and prevents himself from doing so, he also ends up being the one who kidnaps him. So IF he were truly trying to intervene in a way that prevented Mikkel's kidnapping, he's doing a miserable job at it.
What this leads me to believe is that Jonas intervenes with two intentions: (1) To prevent his father from killing himself and (2) to ensure that Mikkel IS kidnapped so that he is born.
If you think that he couldn't have had goal (2), then consider this: if his goal is only (1), and for whatever weak, butterfly effect reason the kids don't go to the caves, and Mikkel is never kidnapped, then not only does Jonas disappear, but so Michael - his past, from the moment he was kidnapped until the moment he doesn't kill himself, also disappears. He would be saving kid mikkel, BUT he WOULD effectively be eliminating Michael: the man whose eyes he just looked into and begged not to do it. So how would that really accomplish any thing like getting things back to normal: he's dead, and his father's timeline is dead, the majority of his father's life is gone.
Relatedly, I think there is more than just a dramatic effect to the anniversary party/day-before-suicide scene in S2E6: THIS is the trajectory of the world that Jonas wants to save...everyone still alive, with their petty -- but really all things considered not-so-bad-after-all -- lies.
Now you might object, wait a minute, if Jonas never follows Mikkel back in time, [but just lives in a town where a few young boys are horrifically kidnapped, These unsolved crimes will pass and then he and his mom and dad can go vacation in the swiss alps etc.,] then he will never form Sic Mundus, and so there will never be ANY time travel at all, so he will actually end up disappearing after all! But given what we know about the show (and I think there's more on this to come S3), his intervening would not change the past before the moment of intervention - Adam and Sic Mundus would still exist - but it would create a new branch of time - an alternate reality - where all the causal antecedents of Mikkel and Jonas would exist uncaused. Look it's no more paradoxical than bootstrapping.
At any rate, I thought it was worth showing that the thread question is not easily dismissed and can give rise to a lot of lines of thought if you don't reach for the first obvious response and move on. It's super unclear how any intervention would create a happy ending for Michael, much less Jonas.