There are so many variables, I don't think it's possible to pin it down to a single reason.
When you say kids on devices a lot, my brain automatically jumps to my nephews, but there are a lot of differences between our families. Our child is a similar age and will watch stuff on tv/youtube but that's about it
Us: two parent, one child family - plenty of adult time/attention, can divide and conquer when needed!
Sister: single parent, 4 kids under 10yrs. She is a great mum but she is spread thin. I have no idea how she does it tbh.
Us: 2x full time working adults
Sister: Not working, on universal credit
Not only do we naturally have more disposable income, we also have a lot of time away from our child and down time is more likely to be spent getting out and doing things as a family because we aren't in switched on parent mode 100% of the time like my sister is.
Us: 2x adults with driving licenses and own cars
Sister: doesn't drive
We think nothing of hopping in the car and going off for a day exploring at the beach, or countryside or wherever (we are NT members too, because we can afford to be), whereas my sister would need to forward plan, budget for and use public transport to get to where she wants to go.
Us: extra curricular activities are no problem, our child does scouts and a sport plus swimming lessons
Sister: older kids are limited to after school enrichment clubs - partly due to finances, partly due to logistics - single parent can't just nip out and pick the eldest up when younger ones need feeding and putting to bed at the same time
There are so many more factors when you drill down into it. We support my sister as much as we can, but she also doesnt live nearby (social housing, had to move away in order to have a roof over her head). Having an only child we will often take my eldest 2 nephews with us on days out in the holidays and they do revert back to being little kids again. We will also look after the younger two so she can do more age appropriate things with the older two. We also pay for swimming lessons.
But she's also a fucking hero in my eyes. 4 kids, on her own, kids dad has fucked off, doesn't see them, certainly doesn't contribute financially. Could I raise 4 kids on my own? Definitely not. Do I judge her for letting her kids spend what I would consider too much time on phones/devices? Absolutely not. I have no doubt that I'd do the same if it was the only way I could guarantee harmony amongst 4 kids in order to get 10 minutes peace!