I agree it'd be nice if there were citations.
I do wonder, having worked in TV for a while, if an entertainment lawyer might have advised them not to do so. Fair use is tricky and lawyers are especially jumpy about it. Citing another source might have opened them up to further complications, although this is only a guess on my part.
As a few people have already explained, mental health relates closely to issues of toxic masculinity. One of the many things "toxic masculinity" refers to is the idea that men and boys should never, ever ask for help. That receiving help of any kind is weakness and people with mental health problems are just giving in to their weakness. Acts of violence and dominance as a response to these feelings of inadequacy and weakness are not uncommon.
All that being said, Sarkeesian's main point was that nearly every single shooting of this kind has been committed by a man. This is a fact. Either we assume that excessive acts of violence are innately, naturally male or we have to begin to wonder if there is something about the way society treats men and masculinity that isn't working as it should. This is what the concept of toxic masculinity is about.
But this is a bit off topic. (I mean, maybe. It gets brought up in every single Sarkeesian thread at this point along with all the other usual bullet points. It's hard to tell sometimes what is "on topic" with discussions of Anita.)
Ah you work in TV? I worked in the music industry and the film industry for some time too. Always interesting to talk to others about it, especially with regards to sexism issues in either industry.