My take, having seen a lot of these posts on yelp, is that people leave such reviews because restaurants are offering something which they are not familiar with, or does not match their notions of "normal" (however narrow that may be). You see this less at restos which serve burgers and pizza, and more with places serving non-American food.

I just took a spin through the couple of Asian places in my town, and they have relatively high numbers of 1 star reviews. Digging into them, what you see a lot of are is complaints like:

"This is the worst Asian food I have ever had because (proceeds to describe exactly how the dish is supposed to be)". Also a lot of complaints about these Asian restaurants being "dirty" (which they aren't - as I'm only reading through places my wife and I go to / order from frequently). It was like this specifically with Asian food in the last town I lived in as well. I recall one complaint about how they romanized a Thai word, insisting "pad see ewe" was misspelled (ORLY!). It's bizarre. Mexican restaurants by comparison, get complaints about the food being too spicy, or the decor (at takeout places no less) being bad. And, of course, "dirty", which again, the places I frequent, aren't.

I can't help but conclude that people who write these reviews are judging things based on their own biases, of which they are not self-aware. A more harmless example is a review from a great Thai/Chinese resto where I used to live where someone suggested the place smelled "musty". Well - it was in a sublevel of a large building ("basement" is the word they used), but it was not in any way musty in the 10 years I spent going there. None of my friends ever took issue, even a good friend with a really sensitive nose.