What offers distributed consensus is proof-of-work, not blockchains themselves. The append-only list of blocks, that is a blockchain, is designed the way it is such that past blocks accumulate work performed on later blocks.

And the only "digital good" a blockchain can make scarce is the token which exists on the blockchain itself, which is completely useless unless it's supposed to act as a store of value. And, arguably, if a blockchain token is valuable because it's scarce, it makes little sense to have an unlimited number of blockchains even if each of them only have a limited number of tokens.