Time Machine - why not allow access to the backup interval?

It's easy to find the answer to the question "How do I change the backup interval for Time Machine." What I can't find....and can't understand....is WHY this function wouldn't be included in the Time Machine preferences pane. I know that asking "why" about Apple's programming may not lead anywhere, but I find this very perplexing. My only guess is that this is one of those "make it as easy to use as possible" decisions, but that doesn't seem like a good answer.Does anybody have a guess? Am I missing something obvious?