Because it's not our place to do so. If someone asks for your opinion that's one thing, but just because someone makes a character or a story, and just has it out there, doesn't mean they want your opinion on it. And the fact that he told you to GTFO, was because he didn't want your opinion, and he's entitled to that. You're entitled to your opinion as well, but as soon as someone tells you to stop, and you yourself don't, then you're crossing over into borderline harassment.
And you're missing the point entirely about Fallout Equestria. It wasn't about how big, or how famous it is. It's a