Because computers and reality don't actually deal with immutable data? I love the reasoning powers you get from it at a code level, but it's simply not a fast way to do things in many cases. Also, many applications do not care about all (or any) interim copies of data.
With respect to web content, what are you proposing? If I got to site.com/product1data and you update the price, we certainly don't want the URL to change. In such situations, how would a versioned system add any value, and how would the UI be exposed?
The price of something has nothing to do with the content. The data that represents the price is a pointer to the content, akin to affixing a new price sticker to the jacket of a book. Perhaps the original published content could have a recommended price embedded in it.
This applies to the names and categorizations of things as well.
As for updates, imagine you're a shopkeep and in the morning you publish a table of prices, titles and content-addressable hashes.
Now, for the whole naming-of-the-things... take your pick: ICANN or Namecoin-like.
Claim ownership of a top-level name and then you can point it at whatever you want.
[not the OP] In your example, the URL name would be a reference to an immutable document with an immutable ID. You can update the named reference to point at the new ID, but the old ID still refers to the old document.
It would also be possible to store and distribute new versions as patches to previous versions by linking between the patch set, old version, and new version.
OK, but how does that fit into how we're actually using URLs today, like how would this change the web? If you browse my product info page, I don't want you linking to a versioned document, in general. In the cases I'm thinking of off the top of my head, I'm not sure when you'd ever want people linking/copying version-specific URLs that somewhat negate the point of updating the page in the first place.
Or perhaps I don't understand "Why can't we look at data that is published on the Internet is the same manner".
The web of today is based completely on "this named thing references this other named thing". When we create links to other content we are most definitely doing so in the context of the content as it is at the time of linking, not some future state. What happens if that data is waaay different or missing? Dead links we call them.
It terms of commerce this is somewhat analogous to bait-and-switch.
In this thread I'm mainly referring digital content as an end-to-itself, not of digital content as a reference to physical products.
As for referencing physical products, be they automobiles or paintings, deriving a direct cryptographic hash isn't possible, but GUIDs are. Cars already have serial numbers. Paintings have signed certificates from experts.
If I'm on a website buying a used car I definitely want the price list to be linking to the GUID, that is, to a reference of the object itself.
With respect to web content, what are you proposing? If I got to site.com/product1data and you update the price, we certainly don't want the URL to change. In such situations, how would a versioned system add any value, and how would the UI be exposed?