It wasn't long ago that you absolutely had to buy hard copies of your software applications to get them onto your computer. Prepackaged software started in the 1970s and '80s on cassette tapes or floppy disks and eventually evolved into higher capacity CD-ROMs and DVD-ROMs. In a lot of cases, say if you wanted to play a game, the disk would have to be in the CD or DVD drive or you couldn't play. You'd also burn any data you needed to move from computer to computer onto CD-R/RW or DVD-R/RW disks. But now you're more likely to move data using little USB flash drives, or send it via the Internet. And lots of computing happens on pared down devices like netbooks, tablets or smartphones, which rely on downloads rather than software installation from physical media.
High-speed Internet in the home has become ubiquitous, and you've likely become accustomed to downloading your software from the cloud even on regular computers, so manufacturers are dispensing with these built-in drives on some of the more full-featured laptops. You can perform a number of tasks in the cloud that used to require dedicated software on our computers, including creating documents, storing and editing photos, and checking or sending email. Although kids might be familiar with putting game disks in a gaming console, even those are moving heavily toward downloads. And a lot of kids today do most of their computing on mobile devices that don't require insertion of any physical media.