Why? Why is consistency necessary for a character to be popular? The important aspects of Superman have been very consistent for decades. He's the last son from a doomed planet sent to Earth who was raised by kindly farmers to use his fantastic powers to fight for truth, and justice. He works as a mild-mannered reporter at the Daily Planet with Lois Lane, the world's greatest reporter, and his pal, photographer Jimmy Olsen.
You can tell interesting stories with or without Superboy, the Kents or using any version of Krypton. Those elements are less important that characters, story and theme.
The important elements to Superman have always been consistent. The quality of the stories, however, has not. That's the big problem.