Probably because of some of the things that Cambridge Analytica stands accused of, or else things they have blatantly admitted to while being secretly recorded: blackmail and bribery of politicians in multiple countries, hacking election results, and even more unethical acts[1,2].
People are upset that their data was essentially stolen from Facebook (it was collected for use in an academic study, then turned around and sold for profit to CA), used by a company with ethical failures as serious as Cambridge Analytica, and then Facebook buried the story. It was two years before it came to light thanks to Guardian journalist Carole Cadwalladr.
Facebook also worked closely with CA during the Trump campaign, even though they would have known by that time that data obtained under the pretense of an academic study had been sold to CA.
People are upset that their data was essentially stolen from Facebook (it was collected for use in an academic study, then turned around and sold for profit to CA), used by a company with ethical failures as serious as Cambridge Analytica, and then Facebook buried the story. It was two years before it came to light thanks to Guardian journalist Carole Cadwalladr.
Facebook also worked closely with CA during the Trump campaign, even though they would have known by that time that data obtained under the pretense of an academic study had been sold to CA.
1. http://www.bbc.com/news/uk-43528219
2. https://www.channel4.com/news/cambridge-analytica-revealed-t...