Ethereum ERC721

ERC721 is a free, open standard that describes how to build non-fungible or unique tokens on the Ethereum blockchain. While most tokens are fungible (every token is the same as every other token), ERC-721 tokens are all unique. (src)
Here is an example of a CryptoKitty NFT data packet based on the ERC721 standard.

{
"id": 1, "name": "Flying Kitten", "bio": "哎呀妈呀！! 本喵爬不更名，坐不改姓，就叫 #{name}！我的表哥是喵星球鼎鼎大名的多啦A梦。 不是什么太高调的事，不过本喵确实和汤姆猫有过相交之情。 本喵和你是不是上辈子见过呀？", "image_url": "https://img.cryptokitties.co/0x5328276603d169165d0f71ca67ccc89c45027df3/1.png", "image_url_cdn": "https://img.cn.cryptokitties.co//0x5328276603d169165d0f71ca67ccc89c45027df3/1.png", "image_url_png": "https://img.cryptokitties.co/0x5328276603d169165d0f71ca67ccc89c45027df3/1.png", "image_path": "", "generation": 0,
}

if you notice the asset is stored off block.

"https://img.cryptokitties.co/0x5328276603d169165d0f71ca67ccc89c45027df3/1.png"

This means that if that link changes you now own a different asset. You can also notice that there are 3 different types of links, each can be changed to represent a different image which would change depending on which link you view it from.
The current alternative to this method is using a "Smart Contract" which requires 20,000 gas for 256bits of data. The above Cryptokitty is roughly 47kb in size. this means that you would be paying 47kb/256b x 20,000gas = 29,375,000 gas. You will need to add 32bytes for overhead which ends up being an additional 16,384 gas. This means 28,391,384 is the total gas bill for the transaction which does not include what the asset may be sold for. 28,400,000 gas converts to gwei at 1 to 49 as of writing this article. That means the gwei cost is 1,391,600,000. 1 gwei is equal to 0.000000001 Ether (Ethereum Token). This means to store the crypto kitty on blockchain with a "smart contract" it would cost you 1.3916 Ether tokens to create. This is is roughly $4,287 as of writing this post on 2/15/2022.
This is a very rough explanation and possibly wrong by a digit or concept but the basic premise holds true, currently creating actual assets on the block chain is prohibitively expensive and is driving the creator economy to use cheaper 3rd party off chain hosting which can be changed at the will of the hosting provider and or government entity.
If we take another similar asset class, houses and draw some similarities. In very simple and possibly partial wrong terms lets explain why off chain storage is a bad asset class. Currently if your standard stick frame house is connected to the ground and is not designed to be modular it is considered a fixed asset and appreciates value. If you on the other hand have a modular home that can be moved and attached to the ground in a new area it will not appreciate value.