@Wiimeiser
The whole “background ponies getting tons of fanon” thing was mostly a product of its time. The fandom was still fairly centralized, and the average fan had a lot more free time to comb through the episodes looking for things. And there was the power of
confirmation bias. If a random background character did something notable
one time, fans were more likely to look for that character, which lead to them noticing other notable things they did. It was a feedback loop.
But the character has to actually deliver. There was a time when Carrot Top was as popular as The Background Six, but she fell out of popularity. There was also a brief period where Berry Punch was “Overprotective Parent Pony”. But they just didn’t give the fandom enough to work with.
Also, the more characters you have, the harder it becomes for a new background pony to stand out. Back in the day, you only had 25 to keep track of, but the number kept growing.
Of course, some background ponies are just destined for popularity:
@Jonny Manz
I’ve been looking for an excuse to say this for awhile now, but I’ve revisited the first four seasons, and of those, I still think Season One is the best. Not because it’s a flawless masterpiece, but because the quality is
consistent, while the quality in the other seasons is more of a gamble.