Why are Apple products so common in mockups?

Inspired by this question: Why are Apple Macs used so much in the graphic design industry?

While browsing through the web trying to find device mockups for my website,

I realized that about 90% of all the mockups were of Apple devices.

For example finding a (flat) mockup of a non-Apple laptop computer is like a mission impossible.

On about every website showcasing their applications (unless it's Android/WP-only) on a device, the device is Apple's.

I think there are better designs out there than only Apple.

Why are Apple devices so popular?