It depends on a case by case bases, some artists out there really REALLY get harassed by fans when they don't get their way, and it could turn very ugly. There a literally fans that will PM or harass artists to 'do this or else' in their story, to the point it's really ridiculous.
Examples I've run into
"If you don't make character A kill character B, you're just a terrible author because not doing that would be bad writing."
"These two species better go to war, and the side I like better win. If not FUCK YOU YOU PICKED THE WRONG SIDE how DARE you make that side the bad guys."
"If you don't get rid of this character I hate I will stop reading. I fucking hate her!"
"If you don't make 'this guy x this guy' canon, you're a fucking homophobic gay baiter"
"The fact that 'this guy x this guy' is canon and 'this guy x this guy' is not means that you support abusive relationships, rape and paedophilia. Fuck you" (couple they're talking about isn't even cannot at all, it's all in their head)
So I understand when authors will react that way under those very specific conditions. Maybe that author has faced this harassment as well and they are growing tired of it? Who knows, like I said it's very case by case.
Aside from the people that will do that, fan theories, shipping and head canons I don't mind, and it's actually pretty fun to see that I have fans so invested in my work. I'll even roll with it letting fans vote on their fav ships (canon or non-canon) for valentines pictures and such, but yes, there ARE fans that will cross the line, and as much as authors do their best to ignore them or handle them maturely they can end up ruining it for everyone.