The excluded family member clause is very much intended to prevent people who are not declared being sponsored at a later stage. It's to encourage full disclosure at the time of application and very much to help to prevent fraud, to protect the health, safety, and security of Canadians, and so on.
For those cases that are exceptional, there is the humanitarian and compassionate application process, which is available to those individuals. That is a safety valve, if you like, for those sorts of exceptional circumstances.