Because Ikea says so…

According to The Economist, IKEA will release a new version of its classic BILLY bookshelf next month, one that’s focused less on storing books than storing, well, anything and everything else. The company is finding that customers use their shelves increasingly for “ornaments, tchotchkes and the odd coffee-table tome,” and less so for reading material.

http://www.economist.com/node/6919139

They’ve realized we don’t need fixed shelves 12 inches high and 9 inches deep. They’ve realized we’re more comforted by the endless capacity of a millimeters-thin box of transistors. And most importantly, they want us to keep buying their furniture. So by changing the depth and height and adding decorative glass doors to their bookshelves, they’ll ensure that the world will still have a use for their some-assembly-required furniture. Go ahead, store your souvenirs on our bookshelf, they’re saying.

http://newsfeed.time.com/2011/09/10/ikea-redesigns-classic-bookshelf-foreshadows-the-demise-of-books/