Having studied the Bronies a bit, I've come to a conclusion: The Bronies forcibly evicted the Tumblrinas from their zone of influence. But it wasn't something they did in a vaccuum - it was the sort of tactical sperging that only comes from deep-seated hurt. Read on if interested.
The conflict between the Bronies and Tumblr went nuclear during the Derpy debacle, which I know
mostly about due to none other than Chris, who was big on signal boosting Save Derpy. For the uninitiated, this was a major attempt by SJWs and Tumblr in particular to get a character who was portrayed as sort of ditzy and out of it as labeled "ableist," and have this character's name (Derpy Hooves) changed because "Derpy" is offensive.
For the Bronies, this was perceived (perhaps correctly) as an attack on the creators' rights to put what they wanted in the show and seen as a potential avenue for unwanted executive meddling (something that's viewed as
haram in the Brony community). Since Derpy was (apparently) some kind of minor in-joke for the fanbase to enjoy, often seen as an embodiment of a nod being given towards its audience, in the same way a Dreamworks picture tries to sneak in a few jokes for the Dads in the audience, she was also rather beloved by the Bronies in general - so they immediately took this as a declaration of
war. If one character could be removed for being "ableist," then the gloves were off and there was no limit to what could potentially be censured. And the Tumblrinas had succeeded in doing so. She was, apparently, all but removed for the remainder of the season and the bulk of the episodes for that season featured extensive corporate meddling, purportedly because of the ball that started rolling because of the Tumblr shitstorm.
Things worked out for the Bronies because they're what kept the all-important cash engine grinding along, and when they started to flag off, Hasbro had no choice but to appeal to the horsefuckers of various stripes who supported them in the first place. This was the first real victory against the Tumblrinas who were fond of MLP, which was soonafter followed by the anti-cult of personality episode which pretty much pointed out the dangers of so-called equality pushers, so at this point, the show's staff was firmly behind the Bronies.
This was when the Tumblrinas left MLP behind, for they had lost it to the Brony hordes. A war fought in secret, by spergs and lunatics, with consequences that mattered only to them.