1. How else would you like the results to be delivered? It is delivered in browser's search bars. It is delivered by visiting Google.com. It is delivered by voice. It is delivered by mobile devices. It is delivered inside my Nintendo Wii, XBOX, PS3/4, and my Nintendo Switch. It's delivered on my crappy Vizio TV via smart apps. It's even delivered in my car. Google search results are everywhere.
2. I think that is kind of the point. However, you assuming Google is being evil by keeping it a secret. That's not fully the case. A lot of SEO companies would love to see how things are ranked so they can beat it on behalf of their clients.
3. They already have an API and if you really want to customize the query, you can add all kind of query modifiers in the UI.
4. As a developer myself in the crypto space, blockchains make a poor curated database for the very reasons why Google keeps things a secret. Anyone with money can pump the reputation of an entry on the blockchain to get better rankings thus lowering the quality of results.
Second, most blockchains can't handle the query load.
Three, dapps cost money to run. I can see a market for users submitting entries. If there are users using it, it might catch on in the submission department. However, this brings me to my next point.
Four, the chain would not have all the websites on the net. Kind of expensive to get it all on there and not scalable.
Lastly, someone has to pay to run the query side too. Would users pay to run a search query and get gamed incomplete results? No.