But they don't do that. These systems are actually distributed, and that's why they work.
But for networks which do, you may want to. For example, only one person may control this name, this domain, this tradeable asset, etc.
Blockchains are an addon to distributed models because they allow a distributed way to prove ownership of something. Say I want to look someone up by name instead of by cryptographic hash, how do I do it? You can't register a name in a Freenet or Bittorrent model.
People are using blockchains for too many things, but that's healthy. It's the only way we can find all the things they're useful for.
When bitcoin became an unfundable space, the VC's and such moved into "Blockchain", which was marketed as the good parts of bitcoin, without the bad.
Unfortunately, the space has seemingly gone on to only emulate the worst parts of bitcoin. Scams, ignorance, and get rich quick schemes. Currently, "blockchain" appears to be targeting centralized, decentralized, mutable, immutable applications. The blockchain movement is meaningless, and appears to be merely the exhaust gas from the bitcoin funding hype.
The blockchain protocol isn't going to 'save the world' - but once a little air gets let out of the balloon, it's going to see a lot of adoption in both financial institutions and back offices in a wide, wide, range of industries. For a world with lots of data and lots of shady actors, it just makes sense.
But I wonder what would drive mass adoption for every day users - aside from a collapse of the current financial system.
For general public it doesn't really matter if AirBnb or Uber or Whatsapp are decentralised or not - we use them because they have reached a point through network effects where they have a ton of users/liquidity, are reliable and have smooth UX.
Also, I'm not sure storage issues are a solved problem for immutable decentralised databases.
Fast global microtransactions could be a useful consumer app but so far there is little need for those. And the UX for fiat->crypto->fiat transactions and wallets is far from what it needs to be for general public.
Overzealousness is unfashionable. Be unfashionable until you're convinced that you're actually wrong.
Bitcoin may be the best-known blockchain protocol, but there many others in active use.
On the contrary, it would be as lightweight as possible. And the transactions in a Block, could point to trusted Oracles outside the Blockchain. And usecase involving streaming content like Movies (the example given by GP) would definitely NOT have the content on the Blockchain.
Rather, just the urls to trusted oracles, in the txn. With the hash of the txn, present in the Merkle Tree in the Block, for verification purposes, so that other parties can quickly verify the block is not fraudulent or tampered with.