Why do Readers get so upset at Spelling Mistakes and Typographical Errors?

Authors often don't understand why a reader liked their book, and yet gave it 1 star or 2 stars or 3 stars, just because there were a few spelling mistakes or grammatical mistakes Surely, if the book is good then it should be a good review Do spelling mistakes even matter? Does a grammatical mistake or a typo really hurt the reader's enjoyment of the book? Are readers just being petty Should...