Why would a contract involving illegal activities not be enforceable?

A contract involving illegal activities is not enforceable primarily because it fails to meet the legal purpose requirement. In contracts, one of the fundamental elements necessary for enforceability is that the agreement must have a lawful objective. If the purpose of the contract is to engage in activities that violate the law, then the contract, by its very nature, cannot be upheld by the courts. This is rooted in public policy, which aims to prevent the legal system from endorsing or facilitating illegal conduct. Thus, even if all other elements of a valid contract are present, the illegality of its purpose renders it void and unenforceable.

The other options, while they discuss the potential issues that can arise in contractual agreements, do not directly relate to the core principle that contracts must have a lawful purpose to be considered enforceable. For instance, the validity of a contract is not solely dependent on the signatures of the parties or their legal capacity if the intent behind the contract is inherently illegal.