When someone is checking out a boy/girl wouldn’t they ask if there are any medical problems in the family as one of the first questions? Now why would you then date a guy who has a potentially life threatening medical problem waiting to happen?
Because unscrupulous shadchanim will sometimes avoid telling about the smoking issue, when asked outright if there are any medical factors, figuring that a potential problem (though extremely likely) is still “only” a potential problem.