What happens as websites disappear? With a blockchain in 2090 you can point to a website post in 2060 as support that your hashes on data posted in 2030 are still valid. That’s useful when preventing people from rewriting history is the goal.
There’s also a size advantage. You can keep a diff on the archive for each hash being posted instead of the full index for every time you post a hash.
But you could do the same thing with any hashes, right? There is no need for a blockchain in the middle.