Alright, this shitposty answer aside, I'll try to give an explanation to figure out what is going on. I'll try to extrapolate what I read about fandoms to MLP, because I personally haven't watched it and surely won't.
Let me put my schizo hat on.
Firstly, anything that blows big like MLP has an extremely important aspect to it, an universe that allows creative freedom [of expression], especially the freedom to make you, the audience, participate and live in it. Spongebob, or any other regular show, usually follows a specific cast of characters that rarely develop centering around locations and an universe that never change as well. You can watch it for jokes, moral values, story and whatnot but you can't exactly participate in it. You're passive as an audience. Meanwhile, you can create thousands of Sonic variants, but you can't really do that with Spongebob, or even Pokemon. Pokemon Universe has an official list of Pokemon designed by it's creators, and it's also copyrighted, which means anything you personally concocted is not canonical, but I'm sure that's not the case in MLP.
You can create a pony that's purely based on your imagination, and it would still have it's place in the MLP universe, even as a background character. It's a pony sandbox.
Another way that I can think of through which you can interact with a piece of fiction is… shipping.
Take Miraculous Ladybug [which I stopped watching because I just couldn't] for example, which has a very notorious love dodecagon going on, with it's audience shipping every character and their dog with each other, writing fanfiction and even erotica based on it. There's enough material for the audience to weave their own fantasies with, and through these fantasies, they find people who have similar tastes and bond with each other through their shipping fanfiction at tumblr, discord or other communities dedicated for a specific ship.
I don't even want to mention the staggering amount of pony porn that exists online.
Another reason that may not be true that I can think of is, MLP is from a decade of deteriorating mental state, with Global Recession going on and USA facing serious economic crisis. I saw an image at another thread in here that had a graph about suicide rates in USA, and you can see a really sharp increase in the suicide rate from 2008 to 2010 upto 5% aPost too long. Click here to view the full text.