Per 
(I want you to remember that this idea wasn't created by me, it was made by not_a_Seagull. I changed it up a bit to fit a narrative I'm making)
In a nutshell: "Boss, some guy made a cartoon about us. Should we fuck it up?"
"Yeah"
"Uh boss, it didn work out as planned but someone else did the work for us."
"K."
In a more described version and I'm sorry for making this so long: In Hell, there is real restaurant there called Dinning in Hell and a man who goes by the name of Adrien Bellitrov has, coincidentally, created a cartoon with the name about it.
They plan on creating a cognitohazardous T-Shirt that would make people go crazy just by looking at it but can't make it there because it's too hot and they can't grow cotton so they decided to get someone else do it for them.
Which is the mayor of New York. New York is the closest place to Hell and he has a lot of power there, so the demons decided to blackmail him into buying a factory and making the T-Shirts. The blackmail are that he laundered money into using it for his election and assaulted a guy whilst he was drunk but for some reason went unreported. He accepts the deal, factory is bought, Vivziepop accepts a contract with him and production follows along with the staff and workers drugged into being unaffected by the Cognitohazard and perceiving any incident involving it as normal so they would continue production. The drug is also tasteless, no smell and colourless.
The Foundation notices this went reports of civilians behaving unusually and they discover the SCP was the cause of it, as well as many Foundation staff and Groups of Interest being affected as well. Due to this, it was ordered by the Cognitohazard Department that all Foundation staff are to be verified for contamination and those that do are to be quarantined. They discover where it's being produced and send an MTF there. The mayor is seen freaking out and just before the Foundation apprehands him, the floor below opens up letting out souls, screams and fire as the mayor is sucked into hell. Why?
Because the Mayor didn't follow the instructions properly. Instead of making people go crazy, it instead made people go interested and paranoid and he failed to handle it properly. As such, the demons are really pissed at him.
After that, the Foundation closes the factory for good, everyone staffed there were given amnestics with false memories and records implanted and the Foundation pursues trying to contain the T-Shirts left.
There is one unsolved problem: There is nothing stopping Hell from trying to get someone else to do the work for them. They already have trouble capturing the T-Shirts, anymore is a nightmare. They can't contain it, nor can they stop them from communicating to Earth. They don't know why they never decided to enter Earth, at least as far as their aware. They have two theories, the first being organic matter can never leave Hell, just like how nothing organic can leave Corbenic.
The second is that they have not developed the technology yet to create portals or they don't have the resources at all or all of the above. The fact remains: The demons won't stop going after people until they get what they want. There is the possibility they've given up but the Foundation aren't taking any chances, so they plan to drive Hazbin Hotel into failure for the sake of people.
They successfully do that (How, dunno yet) and Hazbin Hotel leaves Earth alone.
