You seem to be arguing that blockchain has to magically solve real world physical problems, but paper contracts don't do that either. You still end up in court. Its just a question of how you are substantiating they really signed the contract.
If the problem was about enforcing a signature, you do not need a blockchain, each party to a contract can just store the cryptographic signature themselves or with one or more trusted custodians. That is a fundamental feature of cryptographic signatures not blockchains. And then you need some mapping from legal entities to public keys, but this might as well be a centralized database run by the government (potentially outsourced to a private contractor), after all in many jurisdictions the government already keeps a list of legal entities and metadata about them.