Apple has considered that same question for most other apps. Garage Band, for example, and Apple Mail.
I don't think you should listen to anyone's ideas about why Apple does what it does. But if you want to hear my unfounded speculation: Apple wants to control the out-of-the-box experience for its shiny hardware and therefore includes a variety of apps that >x% of the customers are presumed to use on the first day they have their new shiny hardware, where x is some number and "day" may mean "week" or… well, really, this is unfounded speculation, it doesn't have to be precise.
I don't think you should listen to anyone's ideas about why Apple does what it does. But if you want to hear my unfounded speculation: Apple wants to control the out-of-the-box experience for its shiny hardware and therefore includes a variety of apps that >x% of the customers are presumed to use on the first day they have their new shiny hardware, where x is some number and "day" may mean "week" or… well, really, this is unfounded speculation, it doesn't have to be precise.