Because they are using them to single out individuals (even if those are anonymous) - people expect them to at most use that data privately (ie to see what you

Because they are using them to single out individuals (even if those are anonymous) - people expect them to at most use that data privately (ie to see what you probably like) and to have aggregate things (ie this is the most popular $ITEM on weeknights). And to that that Netflix was condescending and quite frankly rude.