You are correct about the limit of OP_RETURN as @ETFbitcoin pointed out but you are forgetting that the examples you used (documents related to ownership of a car or a house, etc.) has centralization attached to it so you don't need to store the whole document on bitcoin blockchain, but only some sort of link to it like a serial number or document hash, etc. and OP_RETURN's 80 byte limit is more than enough for that purpose.

Here is an example of real world application. Land registry by the government of Georgia using bitcoin blockchain:
https://www.forbes.com/sites/laurashin/2017/02/07/the-first-government-to-secure-land-titles-on-the-bitcoin-blockchain-expands-project/