Because there are times when Doctor Who is not awesome. When it's badly made, or at least seriously flawed. At least, that's a viable opinion that people can express. It doesn't mean that they're negative nancies who are only hatewatching and bringing down the fandom. Every era of Classic Who and Modern Who has its problems, and some of those problems are more or less serious.

Personally, I don't think that this season is terrible, but I do think Chibnall's writing hasn't been up to snuff so far.