When you want to protect your private life...
You confused the decentralization's purpose with social life (maybe I misunderstood your statement, if yes, then please correct me), as the main purpose of Decentralization is to make anonymous transactions without giving control of your, assets, documents, etc. to any other entity and totally depend on it. Like, if you make a transaction, you wish no one knows who is behind that transaction, so you tried to remain anonymous.
On social media, they know what we want them to know about us. But on the blockchain, no one knows who is who or who owns whose wallet.
Social media platforms definitely know about us, but is it true, that transactions on the decentralized blockchain are totally anonymous? because as far as I know, that's not true. And that's also my main point in the post. Like if people are already given their activity data and personal data to these centralized platforms then how can they leverage the benefits of decentralization?
I didn't confuse decentralization with social life; rather, I used your key words to give a befitting illustration regarding a centralized system and that of a decentralized system.
Social media knows what we want them to know about us. It's what I input online as me that the social media captures and keeps as a record of me. I can also decide to live a fake life online, impersonating someone else.
"Decentralized blockchains are totally anonymous?" Yes or no, you are anonymous when you want to be anonymous, and your privacy is protected to some extent when you want it to be.
If you truly want to make a decentralized transaction without risking your privacy, you need to use a system that's totally in line with your beliefs. You can't talk about decentralization while also making use of centralized systems like exchanges. I know there is more of a centralized system than a decentralized system, and most of the claims of decentralized transactions are not mainly decentralized because they keep track of our transaction records, etc.
To some point out, transactions are actually not anonymous the way we think they are. We can completely make that possible without any issue; one can run its own node, use a mixing service, etc. which can guarantee your privacy protection at a higher level.