That's the thing. Even the good games we get given (Rayman, Child of Light, #IDARB, Guacamelee) don't get played (by me at least) because I always have something else to play. I've heard a lot of good things about Massive Chalice, but I can almost guarantee I won't spend more than an hour on it.
I expect Microsoft gets these metrics, and they know most people just download the games and never play them. So rather spend a disproportionate amount on getting in games people do want, they just stick in whatever a publisher's offering to put in for cheap. A token gesture, nothing more. A checkmark on a box for internet comparisons.
I'm not sure if I should be pissed off at this. Years of conditioning mean I'm actually fine with paying £20 a year for Gold now though (especially if it means dedicated servers on first party games / 3rd party exclusives) - these games don't really interest me. If I'd been interested, I'd have bought it by the time it comes around to being a GWG / on PS+.
Maybe these games do legitimately offer something to those who really struggle to afford any games - don't get me wrong, if this had been a thing when I was 12, I'd be in love with it. But now, as someone who can just go to a shop and buy a new game if I want to, there's just nothing there for me. And in the earlier stages of a console gen, there are far more 'me's' than 12 year olds.