A strange thing has happened to Apple (NASDAQ:AAPL) over the past few years. While Apple's obsession with secrecy is well documented, its ever-expanding global supply chain has made it increasingly difficult to keep secrets, especially those related to hardware.

After all, it's pretty difficult to mass-produce tens of millions of devices without any pieces leaking, especially when the entire world wants to know what you're up to. That's why almost all details about new iPhones are known months in advance, and industry watchers are hardly ever surprised at iPhone unveilings anymore. The only types of things that Apple is usually able to keep secret are intangible aspects like names and pricing. Physical hardware is very hard for the company to keep under wraps.

Consider the iPhone 6. In recent months, dozens of prototypes and casings have leaked, likely as unscrupulous factory workers sneak iPhone pieces out hoping for 15 minutes of fame. This one is just the latest in a long string of sneak peeks at what to expect.

With all of that in mind, combined with the widespread expectation that Apple will launch the iWatch this year, why haven't there been any iWatch hardware leaks of any kind?

Possible explanation 1: Apple has succeeded in doubling down on secrecy
The more you try to hide, the more people want to know what you're hiding. Apple is frustrated with its own rumor mill, which leads it to become even more obsessive about secrecy.

To some extent, Apple has come to terms with the effects that its rumor mill has on its financial results. During earnings conference calls, the company frequently notes that speculation regarding possible upcoming products tends to cause purchasing delays, particularly during quarters immediately before an expected launch. The good news is that those are usually just delays, and Apple typically isn't losing those sales to a competitor.

All the same, Tim Cook vowed in 2012 that Apple would "double down on secrecy on products." That hasn't seemed to stop the current stream of iPhone 6 leaks, or to a lesser extent iPad Air 2 leaks. But perhaps Apple has been able to sufficiently insulate the iWatch supply chain, preventing prototypes and casings from seeing the light of day.

Possible explanation 2: The iWatch is delayed
Another possibility is that the iWatch isn't launching this year, and that mass production has not commenced. If Apple is a little earlier in the development process then people have been expecting, there may not be as many possible points of leakage within the supply chain.

Backing up this theory is a report from KGI Securities analyst Ming-Chi Kuo, who has a fairly good track record regarding Apple rumors. Kuo believes that Apple has run into manufacturing challenges with the iWatch, and as a result it will be delayed until 2015.

While Tim Cook has promised investors that Apple will enter new product categories in 2014, and agrees with services chief Eddy Cue that this year's product pipeline is the strongest in 25 years, there could be factors outside of Cook's control such as manufacturing challenges.

Possible explanation 3: There is no iWatch
This is the most unlikely scenario, but what if there is no iWatch? Or rather, what if the iWatch isn't actually seeing a launch anytime soon? Recall that shortly after Steve Jobs' death, everyone was widely expecting an Apple TV set to launch based on comments Jobs made to biographer Walter Isaacson.

Yet, here we are almost 3 years later and no Apple TV set has materialized. Apple appears content to push its TV and living room strategy with the current set-top box offering, which is actually probably the right call anyway. The TV business is not attractive, and Apple can accomplish its ecosystem strategies with the current device.

Regardless, it's possible that any iWatch currently in development may not meet Apple's high bar for its products, and perhaps the company isn't planning on releasing the device anytime soon, if at all.

Again, this explanation is the least likely, as Tim Cook is a purported fitness buff and the wearables trend is too important for Apple to sit on the sidelines.