I feel like, after a very densely populated fall-spring last cycle for games (TR2013, FC3, Hitman: Ab, Sleeping Dogs, BSI, Metro: LL, etc) there just wasn't a lot released since that has really excited me. So it's not just weak sales, it's that there's not much I'm looking for to go on sale. 50% off wasn't enough to make me bite on Papers, Please. A good discount might make me try Kerbal Space Program since, despite its "early access" status I've seen a lot of people saying good things about it. I doubt it'll hit the 75% point though to make me take the plunge.
I bought Aliens: Colonial Marines for the two dollar lulz and that's been it so far.
Oh, and Secret of the Magic Crystals has (had?) a promotion where you can buy the Android app on sale for 99¢ (all Amazon app credit in my case) and get a free Steam key for it