Because you can’t write if you can’t read. Sorry, but it’s the sad truth. Too much of the world thinks they can get away with one book a year and expect to win the Nobel Prize.
Think of it this way. Can one write music if he never listens to it? Can one paint if he has no exposure to other people’s art?
Definitely, but no matter how good he or she is, eventually, that person will suck at whatever they’re doing.
Why? Because without external inspiration or backup, you have no idea how to get better, and what you write will never be published, because it’s not even close to being literature.
That’s one of the things that separates jobs such as engineering and programming. Writing is 100% pure art.
So take the time, whether monthly, weekly, daily, or bi-daily to go to the library and read. Better yet, go to the library and write! (That’s actually an amazing idea. I should start doing that more often.)
Sign up for magazines. Register Google Reader. Read one Wikipedia article a day. Skim the front page of Yahoo.
Go. Expand your vocabulary. Take your notebook with you and write down every single idea that you have.
Surround yourself with material. You’ll be bogged down with reference and inspiration, you won’t be able to stand it. You’ll love it, trust me.