Basically two reasons:
1) profit taking - the day traders can see a decent turn and close their positions.
2) many industry analysts still think that Intel have matured as a business, see little significant growth in the future and the current marketcap represents 'fair value'.
Holding intc for capital growth based on recent years performance just hasn't been that smart a decision, so the sooner it grows up and starts paying some serious dividends the sooner you might see this reach the giddy heights of $30+ again!
Alternatively, it would be nice to see some action behind the rumours of an active US investor/corporate raider stalking them who intends to stir the situation up, ask some serious questions of the board, and perhaps then go for a breakup..then we might see $30+ again.