Quote from MattF:
because many aren't. Tons of scam posts on monster.com now. Others may post to merely collect apps. *maybe* if someone exceptional came across, they'd look at it further, otherwise the company really isn't hiring at the moment; more for the future.
Some others may be hiring, but then the position gets cut in the budget...or they're not sure yet if it will officially exist.
It's almost of a perception issue at times...either way one has to wade through more crap then ever before to get through and find a worthwhile position...or fight with far more people.
Of course, still other people are stupid and don't know still how to properly apply for a job, or make themselves stand out from the ever growing crowd.