My version of Horizon lore is a bit more twisted, where the Horizon officials are completely oblivious to how much the rest of the world hates them and their festival, and how they ruin any country they go to.
The festival sites are set up and things seem great at first, with tourists coming in and local jobs being created... but then they get going, with loud, ****** repetitive music playing 24/7, keeping people in the area awake. The teenagers think the festival is awesome at first, but then they realize it never ends and they are trapped there, and turn to drugs to keep the party going. The confetti from the 24/7 confetti canons builds up in the local drainage systems and creates blockages, and gets washed into nearby lakes and rivers, where it chokes fish.
Then you get the incoming drivers, with a ton of douchebags who think they are coolest person at the festival screaming around in their loud cars blaring stupid horns and crashing into everything and using up all the gas, which drives the price up. Pretty soon the locals either can't afford to put gas in their own cars or are too afraid of getting crashed into to go out, and the few that try are late to work because some moron in a luchador mask driving a pink Lambo pushed them off the road while trying to figure out which button to push to use their new "DAYTONAAAAA!" quickchat... or just flat out get killed in head-on collisions by people trying to set new speed trap records.
The festival organizers are so self absorbed they keep building cross country tracks without asking the locals, and as a result tons of crops get destroyed and livestock is perpetually escaping through damaged fences. Every day, thousands of small trees and cacti are destroyed and eventually things struggle to regrow before being run over by another AWD swapped muscle car. With a Monster livery, naturally.
Ever wonder why there are no cops? The local government had to cut funding for the police force and redirect it all towards replacing the guard rails, road signs, and street lights that the racers are perpetually crashing through. Ambulances don't even bother to go out anymore, as they can't make it back to the hospital in one piece.
In all seriousness, I would love a fan-made "pepega" style mod for a Horizon game where you start off and everything is normal Horizon, and by the end all of the pretty grass has been run over until it is mud, no one bothers rebuilding the stuff that is constantly crashed through, the roads are empty and all the houses have for sale signs in front of them as people flee the area and the whole thing starts to look post-apocalyptic. As fuel gets burned up the price keeps going up until it is unsustainable to race and only the richest are left driving cars. All the festival party goers are dying of drug overdose and dehydration, sewer systems are backed up with confetti, and garbage disposal has gotten out of hand with all the broken stuff being piled everywhere and burned, destroying the air quality and making everything smokey.
The final "mission" could involve the few remaining local farmers and business people revolting and raiding festival sites and attacking Horizon organizers with pitchforks and weedeaters, chasing down the DJs and smashing the stereo systems. You have to use the last of the fuel that you paid $800 a gallon for to drive around to the festival sites to pick up key staff in a widebody Aventador limo with chameleon paint and a generic Forza wing, and then escape to the airport while being chased by angry farmers in tractors, landscapers in pickup trucks, and angry parents of teenagers who died trapped at the festival in minivans.
Then in the final cutscene aboard the jet a girl in a chicken suit sits back and asks a guy in a gingerbread man outfit and a crash test dummy "gosh what was their problem? That was crazy haha... So where to next boys?"