Imagine if a notary, post office, etc. set up a signing service: relational database, basic signatures for user-submitted hashes, etc. Not quite as good but much cheaper to run and much easier to have trusted by a court — I suspect most users would see no additional advantage by adding a blockchain.
The centralised approach described requires that one trusts the database administrator. For a lot of things (probably the vast majority), this is good enough.
For the rest, there's decentralised distributed immutable ledgers.
Trying to explain something like Bitcoin just seems like you’d have a hard time meeting reasonable doubt standards in a dispute but that’s not the only model.
In July of 1610 Galileo was still making discoveries faster than he could publish descriptions of them. On the 25th he discovered that Saturn was apparently situated between two smaller companions that always moved together. Wanting to establish his priority of discovery, but not yet ready to reveal what he had found, he sent to Kepler (and others) the following jumble of letters, which he informed them was a coded description of his latest discovery (...)
If I made a groundbreaking discovery today, putting a sha-256 of it into the blockchain would be a very good proof later on that I actually owned it at this time.
But beyond that I agree with you. My (non-technical) girlfriend is looking into cryptocurrencies lately and she watches tons of youtube videos about it while doing her research (TEDx talks and the like). Easily 90% of the claims of "blockchain is going to revolutionize X" are easily dismissed either because the blockchain can't do what the person claims or there's an other, often simpler solution to this same issue. "Use the blockchain for food traceability", "use the blockchain to validate critical equipment firmware" etc... It sounds good as long as you don't think about it for more than 10 seconds.
The problem is that in order to realize that you need to have a rather deep technical knowledge about how the blockchain works, something 99% of people investing in crypto probably lack.