...and they got a message saying their behavior was acceptable because the person they targeted with it got banned while they didn't.
No, they didn't. The Instant Feedback Report notification doesn't say anything about the reportee's behavior; just that a person they reported in a given match (which it doesn't specify what player or which match) was punished. It doesn't tell them that their behavior was acceptable.
Funnily enough noone I reported in the past week was punished either...
Just because they didn't get punished doesn't mean your report did nothing. This is really something that a lot of people need to understand - not everything is going to have an immediate, tangible effect, and just because you're not getting pop-ups left and right every time you report someone, that doesn't mean that the IFS isn't working or that Riot doesn't give a shit.
But then, I don't think you'll really care, given that you openly state that you've given up on improving and will continue to be toxic - despite that meaning that none of your accounts will last.
Each of these punishments have been back-to-back, with Riot seemingly keeping an eye on me following each one so they can slap me with another the same night...
...Why should I feel sorry, or any remorse whatsoever? I don't anymore.
At that point I simply realized it doesn't matter and there's no point trying to improve or be a better player.
Man, it's almost like if you go out of your way to be toxic, you're much, much more likely to get reliably punished.
You'll have to pardon my sarcasm, but seriously. Of course you're going to get more quickly and reliably punished if you just throw reform out the window. You have zero right to complain about how quickly you're getting punished.
...and the quality of players I'm being matched with has seen zero improvement whatsoever. In fact it seems I'm being paired with more unhealthy teammates as time goes on, leading to further punishments. I would almost call it entrapment.
And your suspicions are incorrect. Riot has openly stated that they're against Prisoner's Island-type systems, so if you're running into toxic players, it is entirely coincidence.
For that matter, it is an unfortunate side-effect of the Free-to-Play model that Riot doesn't have any foolproof way to strictly prevent toxic players from coming back, which tends to result in those baseline MMR's of new accounts being fairly polluted with toxic players.
At the end of the day, if you're feeling "entrapment", it is largely your own fault, since you don't intend to reform, and your continued toxicity will lead to a perpetual cycle of getting banned, making new accounts, and consistently dealing with other toxic players who are doing the exact same thing.
Whatever the case is, I think RibbyTheButcher was right. Punishments aren't designed for reform, and any desire I had to do so is fleeting because of them.
I would take their comment with a grain of salt, given that they make a sweeping generalization of the playerbase in the same breath as they try to criticize the system.
At the same time though, I have to ask; how do you think punishments should provoke reform? At the end of the day, all they can do is place impetus on a player to stop misbehaving and acting out, and even that much can very frequently fail.
Hell, you got permanently banned, and after the 14-day ban, you were explicitly warned that any further misbehavior will result in a permanent suspension of your account. They straight-up told you, "if you break the rules again, you're losing everything" - and you still went ahead and broke the rules. If the threat of losing your account isn't a potent enough trigger for reform, what else could possibly help?
Apparently these people who don't get punished when I report them despite their toxicity are a thing, so I should just learn how they get away with it.
Here's a spoiler alert; they don't. No matter how clever someone thinks they are, how well they think they know the system, they will ultimately get punished. Just because the punishment doesn't happen immediately doesn't mean it will never come, and thinking that you could possibly learn how to be toxic and get away with it is a fool's errand.