There's a recap of it on Reddit's Wikipedia page: https://en.wikipedia.org/wiki/Reddit#2015

Basically as I understand it, Victoria Taylor used to handle some significant portion of the AMA coordination. She liaised with celebrities and notable people who agreed to do an AMA, and she was a part of what made AMAs something pretty special back in the day. When they first became popular there was nothing else quite like them. They felt organic, authentic and unfiltered. They felt like they could give you as a participant a level of access to these A-list celebrities that had just never existed before. Since then there's any number of other more corporate-controlled media clones that sort of fit the same sort of mold, but not really. For example, Wired autocomplete interviews feel like they fit the same niche except with all the rough edges and community participation filed off. I.e. "we can't trust you animals to ask questions without throwing out a racial slur so we're going to let the autocomplete algorithm ask the questions instead."

I think Victoria was also well liked by the mod community, and I get the sense that she had become a point of contact for them when they wanted to express a grievance with Reddit admins/management and weren't get any traction through the normal channels. I had been a regular Redditor for several years when she was fired, and I remember the blackouts that occurred back then. It was very similar to the API change blackouts that occurred recently, with subreddits going dark in protest of Reddit corporate decisions. At that time Reddit had an interim CEO named Ellen Pao, and she took a huge amount of the heat for the decision. It got rolled up with the heat for banning of a number of offensive / edgy subreddits (e.g. /r/fatpeoplehate), so it's kind of hard to tease apart how much of the ire was related to Victoria's firing and how much was related to the banning of those subreddits. Ellen Pao didn't survive as Reddit CEO much longer after that, she resigning shortly after and was replaced by Steve Huffman.

The whole event with Victoria's firing really presaged the current situation with the API changes. I'm not sure if it was the first time where Reddit seemed to be turning toward the corporate, but it was certainly the first time where I noticed that change in direction.