Because revenue is easy but growth is very, very, very hard.
Any idiot can get signups when they have millions of VC money to burn. Getting people to actually pay you more than you're spending on user acquisition is infinitely harder.
Can you name 2 or 3 "idiots" that have done what you suggest?
Pinterest. Groupon. Reddit. Snapchat. Instagram. Youtube (for many years). Twitter took a long time to make money. Most news sites have a hard time, which is why WSJ is paywalled (as mentioned in the article). On the "smaller valuation side", we could say FriendFeed, Zite, Hot Potato, Beluga, GroupMe, TweetDeck, Dodgeball.
It's much harder to than you may realize to monetize.