It gets that way when you win/lose WAY more games than the system expects you to.
It gets that way for almost every player, it's just normally not that significant. LP is not connected to MMR at all, it's a system that floats on top. There are no points at which the two systems check each other for accuracy, to my knowledge, so theoretically there are far more people with incorrectly represented ranks than correctly represented.
Here are some quotes I pulled from what you linked that seem relevant. I'm going to touch on each, but the basic premise is not that I don't understand the system; I don't understand why the system is designed this way.
There is only one factor that affects the amount of LP you get: the perceived difficulty of the match, which is based on the MMR difference between the two teams.
In other words, LP is affected by MMR difference. Why not utilize a direct relationship as opposed to a two-way matching system? Why doesn't your MMR rise/fall at the same rate as your LP when you win or lose? I understand the calculation method but...why?
If your MMR is significantly lower than where the system believes you should be for the division you are in, then your LP gains will be reduced and LP loss will be increased. Alternatively, if your MMR is significantly higher compared to the average your current tier or division, you will gain more LP and lose less. You may even skip promotion series or advance multiple tiers if your MMR significantly outweighs your league.
This makes very little sense. If you can skip divisions, why bother slowing progress down so significantly with the divorce of LP and MMR? You could just hook MMR and LP together and end up with a far more accurate system at a very similar pace, without needing to worry about MMR being significantly different from your LP's portrayal.
Your league placement indicates your progress against a set of opponents who are similar to you in skill level, but it doesn't restrict competition solely to players in your league.
This is a fluff statement, in my mind. League placement shows your progress against a completely random group of people that share similar LP numbers (but not MMR!) and doesn't restrict who you play against. Why even bother with the Leagues if this is the case? They have literally no impact on your overall standing, according to this sentence, and are a false indication of your MMR.
The system does not use your LP, progression status, tier, division, or any other piece of League information.
Then why bother with LP? If it has absolutely zero effect on matchmaking, why is it the factor that's used to show yourself and other players your skill level?