I think when something is an issue for 90% plus of children (which I think this is probably is in some form), then it's not something we can blame entirely on parenting.
I seem to have struck lucky with a child who didn't want a mobile phone, but he was one of only two or three children a year of 200 at school that didn't have one. I can see that it's hard to deny your child something that every other child has and phones are useful when your child starts becoming more independent. I certainly wouldn't do a long journey without my phone myself. We obviously managed without phones as children, but if your child is going to school on public transport, I totally understand wanting them to have a phone in case of problems.
The apps and websites often have good (or relatively harmless!) parts to them e.g YouTube has tons of brilliant educational videos. There is no easy way as a parent to give them access to the good parts without access to the more harmful parts. You don't want to be a total killjoy and never let them play a computer game (plus playing games with them is fun!). Schools require internet usage for homework. You end up in lots of awkward grey areas. Is watching a video about building logic gates in Minecraft ok? If so, then what about Minecraft videos generally? You can't pre-vet everything they want to watch and then supervise them closely to make sure they don't stray from that.
It feels different from smoking/alcohol because there are so many grey areas and there isn't quite as clear evidence as to what exactly is harmful. Ideally you try and prevent your children smoking and drinking alcohol with education and setting a good example rather your wrath. That's trickier with social media.
I think the current proposals are non-ideal but a bit of a desperation measure because nobody has come up with anything better.