How relative can be "Blockchain" and "Social Network Applications"?
I think you have pretty much answered the question yourself. The only use case I can think about for implementing social network on a blockchain is if you are hosting content that is illegal (connecting the likes of drug dealers, child porn makers etc.). In that case you can be assured that since there is no single point of failure, the law enforcement agencies cannot shut you down. Consider Silk Road Dapp on Ethereum. For all other use cases, it is redundant.

The current hype of putting everything on the blockchain is a gross neglect for the basic engineering design principles. Blockchain has a very specific use case: Ensuring transactions are valid and no double spend occurs. It should not be used to store your house land record, your marriage certificate or how many times you shower in a day. As you store more and more redundant data on the blockchain, it would get so bloated that a normal user would refrain from running a full node. What's the point of calling your blockchain as a decentralized system then?

As far as my interactions go with normal people, they do not mind seeing advertisements next to their social media feed. Some just block it off with ad-blockers, other love the recommended shopping lists it shows them. The mere concept of paying $0.1/tweet is absurd and pointless. You can build pretty elegant software solving the real life problems that are currently being faced by people. Putting everything on blockchain is definitely not what is going to solve them.