I believe the airlines, I suspect the cameras are there because it's a feature not enabled, and it is often cheaper to simply leave unused electronics in things than redesign them to remove it.
There is perhaps an argument about "what if someone hacked the system" but I see that as different, what value would an airline truly get by monitoring the pax at that level? The airline already has your real name, age, and thanks to co-branded credit cards and frequent flyer points earning they also know how rich you actually are and what you like to spend your money on. What you thought FF points from shopping and credit cards are "free"? They are potentially the most expensive thing you'll ever do, those offers for toasters are no accident.. They don't need to collect additional data to see that you spent 2 minutes looking out the window whilst the movie was playing, they already know everything about you.
During the flight itself I know that they record IFE views by individual pax, but that's more about getting stat's on which movies are popular so they only pay licensing costs for things which are likely to be watched, and no doubt they track how popular the chicken was compared to the fish for the same reason.
As for USB chargers being more than they are, that's a pretty old hack (in IT terms, ironically the attack was first used at a hacking convention, aka the place where you'd think the attendees would know better than to fall victim). A good number of charge cables these days don't even hook the usb data pins up for this very reason.