It's not about having "N hours to keeping them entertained", it's about choosing the mode of entertainment. Kids got along just fine before tablets, and in many cases were more social and had more exercise.
I'm not against kids playing games etc - I certainly played enough in my youth - but there are better things than surrounding them with screens 24/7
Nobody is saying that surrounding them with screens 24/7 is the answer. And it's not like other modes of entertainment are without risk. I have to supervise my kid to some extent no matter what he's doing--playing with neighbor kids, making something with glue, paint, scissors, etc., or playing games on the tablet. This isn't about parents abdicating their duties to the tablet. This is about an unreasonable system.
If the intersection by my house had no stop signs, I'd go to the city council and say, "Hey! There's an uncontrolled intersection right next to my house, and I can't let my kid out the door without direct supervision, or he could get hurt. There need to be some stop signs there!" That's the answer, not "pay closer attention to your kid you lazy parent!"
Likewise, if I can't let my kid play on the tablet without hovering over his shoulder the whole time to make sure he doesn't accidentally buy $99 worth of fooberries, the best answer isn't to just suck it up and watch him play his game for an hour. The answer is to put in some damn stop signs, and that's all people are asking for here.