Printing an ad is one thing. Printing an ad that actually does something is another. Hopkins was well know for his work that inspired immediate action. This is partially why he was so likely to use a coupon or limited time offer. He believed that it help consumers avoid procrastination.
This is also a major requirement of his scientific advertising method. If there is no call to action, there is nothing to test. We need to know where our success comes from. It really is the only way.