Because the call stack does not include the value of function call arguments. A good error message does include the call arguments values relevant to the error

Because the call stack does not include the value of function call arguments. A good error message does include the call arguments values relevant to the error AND those of the relevant variables. But I agree it takes upfront effort and often also need adjustments when debugging an issue later (i.e. adding more info to the error message and rerun).