Bias: I'm coming up on forty, so my experience of being a kid in high school was twenty years ago. I work with a few "kids" in their early twenties, and have a few family members in their teens and twenties.
Parenting as in "process of raising and educating a child from birth until adulthood" and the use of phones/tablets as parenting tools are a HUGE factor.
When I was young, under 8-ish, my parents were very strict on following rules. My bother and I could watch TV, play video games, run around outside with impunity given that there were no other obligation but if we were told that the TV goes off at 6 for some reason and we resisted then the TV was unplugged for the next couple of days. Talking back would mean the rest of the night with no toys, single user devices like the family computer had a set time limit, going over the limit would have your next turn revoked. It was also instilled in us that the authority of parents extended to other family members and teachers.
By the time we were in our early teens my parents could go pretty much hands off. As long as all school obligations were completed we were free to come and go as we pleased, it was pretty awesome. I'm not sure it was the ideal approach to parenting but it made two teens who never had disciplinary issues in school and could be trusted not to go drunk driving or start smoking pot.
I've seen very little of that type of parenting in the past 20 years, particularly at a young age. Outbursts and insubordination are more likely to be met with a conversation or an argument and entertainment is rarely deprived as form of negative reinforcement. Phones/tablets are also used as a pacifier, which presents a big problem. The internet has been geared by businesses towards grabbing, and holding your attention by manipulating your emotions. This is not great for adults but I suspect this is pretty bad for kids who are still learning how to understand and deal with emotions in general.
And it's not like parents want to raise kids who are pricks but there are WAY more pressures on parents now than there were 30 years ago, enforcing rules without resorting to violence is stressful and difficult. Plus there have been some pretty ridiculous financial stresses, employers want more time from employees, our health care system is a nightmare, no one can afford to be a stay-at-home but no one can afford childcare either. And you still have the 24/7 assault of businesses trying to manipulate your emotions and keep you permanently anxious.
All of this gets you an emotionally unstable kid who is used to getting what they want either immediately or after applying some pressure to an authority figure, and parents who are too burned out to and unsupported to do anything about it.
tl:dr: old man thinks things were easier 30 years ago, that is bad for kids now.