Do any of those "alternative" social networks have a built-in currency?

Are they using blockchain-technology under the hood? (aka private keys)

Do they have an internal market for converting to stable coins?

Do they have a DPOS governance like Hive?

Do they have as many witnesses as Hive for decentralization?

Are there any other factors at play?

Ignorance. People don't understand why Hive is superior.