Playing games on those screens sucks: the controls are bad, the input latency is bad, the screens are usually pretty low fps (30 in the best case), and the hardware running the games is underpowered.
Playing games on your phone is better than the screen, watching stuff is better on the screen, so while this may be a cost cutting measure I'm fine with it for the most part.
I don't like the IFE screens because of terrible hardware (unresponsive screens) and software. I always use my own device.
But you're right -- I generally don't even want to interface with the IFE and either leave it in map mode or off, if that's possible. Occasionally there's a film I'd like to watch, but never enough to watch on the seatback. On my ipad, OK.