I find threads like this fascinating; they really showcase how differently households run. What stands out most to me are the posters who seem genuinely baffled that anyone could be doing things differently, despite generations of families managing just that. I was raised by two working parents and still barely had the TV on, and my children are having the same experience. We do not own tablets, and our smartphones are tools for comms and navigation, with no games or entertainment apps. In answer to all the 'but how are you doing it?!' posters, I wonder if because we have always lived this way, it is easier than trying to change habits later. Not to say it's not possible, it's just going to be difficult listening to whinging and negotiating etc, and mostly people tend to avoid difficult if they can.
The big difference is that low screen used to be the default, not a choice. Television (and especially children's programming) was limited. Now, screens and child-focused content are constantly accessible, so for many people they have become the easier option. It is similar to ultra-processed food; the more available something is, the harder it is to avoid. You have to actively resist something designed to be appealing and addictive.
It is easier (imo only in the short term) to put a child in front of a screen to keep them quiet. It is simpler and quicker than packing activities or finding other ways to entertain them. In the same way, grabbing a packaged snack is more convenient than preparing alternatives. Humans tend to follow the path of least resistance, so it is not surprising people choose the easier route. You can see this even in childcare settings and schools. My children went to a largely outdoor forest school, and even there screens were occasionally used.
The challenge comes later, when they try to cut back and realise how difficult that is. Which unfortunately the more we as a society learn about the negative effects of screens (not just on young brains either tbh) the more you can see how important that is. But the OP is right, it's irritating that this falls to parents and families rather than the people designing and providing the produce. Feels like economic greed always wins out. It's a bit like stoically washing out those yogurt pots so they can be recycled, which when compared to the huge impacts of commercial and agricultural causes of climate change feels like a tiny drop in the ocean really. Making the better choice (be that screens, UPF's, environmental choices etc) an feel like you're constantly working against the tide. It is exhausting.
I do not think TV is the devil; two things can be true. We enjoy it together as a family for films, sport, and nature programmes. But even then, I notice the pestering for more increases afterwards, and that is with children who have always had limits. If you are trying to rein things in after being more relaxed, it will take a lot of determination, something many tired, overwhelmed parents and teachers understandably struggle to maintain.