As in every other walk of life, there are those who play by the rules, and the spirit of those rules. There are others who bend them, and outright cheat, lie and steal to get ahead.
Pirates steal from authors.
'Farmers' steal from amazon, and their attempts to hide their 'illegal' pages read by adding in the odd legitimate book to their system hurts those authors reputations.
'Stuffers' game the KU Amazon for their own advantage. For examples search the new 'loophole' of adding 'romance compilation' to a stuffed book.
This article explains the facts in an open letter to Amazon's boss.