Said parents and guardians cannot protect their kids all the time - they have their own responsibilities like work. Most kids go to school during the day. The few that aren't grow up in homeschooling systems or cult-like environments, which are their own problem.
I frequently see this rhetoric (parents should look after their kids) from naive people on the internet that clearly don't have kids of their own (or don't have teenagers, or don't live or let their kids live free, etc)
But we went to school 10-80 years ago and even 10 years ago, school was very different back then. Apparently now there's a lot more technology involved, and kids can bring their phones and use their phones all day which is why there's a backlash. When I was at school, phones were mainly used for texting (or calling, but not at school) and if you were (un)lucky enough have one, you had to put it in a locked drawer of the teacher's desk at the start of the day.
I frequently see this rhetoric (parents should look after their kids) from naive people on the internet that clearly don't have kids of their own (or don't have teenagers, or don't live or let their kids live free, etc)