Writing is hard.
Sometimes reading is hard, too.
Reading bad submissions is especially hard. You know the author has high hopes for their book, but your taste and theirs doesn't match. Enh.
I used to get so mad when I'd hear about a rejection that said, "I just didn't fall in love with it." I used to think that was lame. I mean...what does it mean?
Editors don't open a submission with malice. Honest. At least, I don't. I want to find a great story. I want to love the story, be unable to stop reading until I've gotten to the end. I want to make the writer's dreams of publication come true.
The thing is, taste is subjective. And what you might love, I might not. Take sci-fi, for example. You might love it, with its shiny surfaces and amazing gizmos and gadgets. I respect that. But it's just not for me.
That's something I say a lot. "It's well-written, but I'm not the editor for this book," or, "I can see how this would appeal to lovers of sci-fi, but it's not for me". Or...'I just didn't fall in love with it." Ehn.
Or maybe it's just my sinuses. Remember Tony Randell's Felix Unger from The Odd Couple? Enh! Enh! Enh, enh!