Blockchain's implications go against their primary motives and sources of income, which is people's data. Twitter and Facebook do not want people's data to be protected and secure. They make money from it.
Advertisers get access to sensitive consumer information through these social media platforms in order to create targeted ad campaigns. Consumers do not get paid for their information, since they agree whether they know it or not to give it away for free to platforms such as Facebook and Twitter.
https://bitcoinist.com/decentralized-social-media-safer-facebook/This is why decentralized social networks are the future.