Why is this better than just signing it with any private key and sharing the public key? Why do you need to involve a blockchain and I assume transaction fees as well?
People using Ethereum often also use blockchain based domains which makes it easier for non-technical people to be more certain about endorsements. Ethereum leaves the implementation of how something becomes endorsed by a domain up to the owner(s) of a domain.
> Why do you need to involve a blockchain and I assume transaction fees as well?
This is more dependent on implementation. Just endorsing something does not need to be on chain, so there does not need to be fees.