While I don't approve of the way the community behaves towards him. The simple answer to why can be summed as looking at what Riot Repertoir is doing v.s. CertainlyT is doing.
While there has been some dissent about some of the changes to Garen, Repertoir has been addressing a good chunk of it, he's been proactive and he's asking question and maintaining a dialogue on the forums.
To sum it up, he's showing a genuine interest in what players want, which is something that this board hasn't seen in an extremely long time.
Look what has happened as a result: forum users are basically kissing the ground he walks on, threads are popping up asking him questions and praising him, he probably just attained one of the largest fan bases of a riot worker in the course of mere few days.
Why? Because he listening and posting, something which has been said time and time again that the forum really wants/need. The thing is, they weren't kidding, they just want someone to be proactive, and now look, the forums users are happy and feel like their opinion is being heard. All because of literally just one riot employee who started doing this not even a few days ago.
Meanwhile, CertainlyT? nothing.
I get that he doesn't respond because he just gets abused by the forum users, but he has no one else to blame but himself. He essentially sticks his fingers in his ear and screams lalala in the perception of most people on this forum when it comes to feedback.
And look at what has happened, he has several champions associated with him that are despised widely by the LoL community, all of which could have been avoided quite frankly if he had taken the time to listen to what players were saying. ESPECIALLY in the case of Kalista....dear lord.
You don't need to necessarily agree with the feedback, but being responsive is critical, having an open dialogue is critical.
CertainlyT has done neither of those two in a proper manner in a long time, to the best of my knowledge. He shuts down any dialogue, essentially with the I know better than you attitude.
Quite frankly, you know what company he reminds me of? Runescape. Look what happened that game, they told the players they knew better than they did. Forced a heavily unwanted change onto their players in the form of Evolution of Combat. Players voiced their opinions and told them this was not the right move, right up to the very day of release, and all through it, Jagex continue to say, we know better than you and we are going to do this anyways.
Subsequently, what happened next? Their player base drop to 1/5 of what it used to be. They had to break their biggest promise of not bringing micro-transaction into the game in order to keep the game afloat, and in general, while the game is still going, it's a ghost of its former self.
CertainlyT embodies a lot of that...and it is really worrisome, having seen it happened to one game I loved dearly, I don't want it to happen again...but CertainlyT's attitude is the exact same as that JAGex had.
And it frankly really fucking sucks cause despite all said and done, the guy does have some seriously good ideas for champion development,
Yasuo, the wandering samurai? Brilliant thematic and gameplay concept.
Kalista? Again, the notion of a relentless hunter pursuing their opponent and torturing until they finally execute their target? Fucking awesome concept, and on paper, her gameplay looks amazing and does a beautiful job of reflecting her theme. If it wasn't for the fact that her kit is just unfun, she honestly would go down as being one of the best thematically designed champions I've ever seen...unfortunately, her theme has driven her god awful passive.
He's an amazing champion designer, but he needs to realize they can't just be shoved onto the playerbase. Have a dialogue about champion development and you'll see the communication improve.