I think it's more the case that many parents are not tech savvy enough to even know that's possible or how to do it. Also, this create a safety net which seems too fragile, as you just need one family that doesn't do it to potentially expose all their friends.
It's no different to the phones for toddlers at school - they can, they know how, they are just even more affected by FOMO, peer pressure and judgement than children.
The other excuses are all just cope - little Timmy will just find a way around the blocks is true. Little Timmy can also get Heroin if he really wants or just one family might offer all the kids a hit on a crack pipe but it isn't an excuse to keep a needle, pipe and some fresh gear in the living room.
And as another commenter points out, this also requires parents to unionize and enforce blocks together. (”Block en bloc” if you will.) Otherwise Timmy just uses Johnny’s phone to watch XXX videos.
I’m not arguing for either side, just pointing out a reality of the situation.
Who are these six year olds with cell phone plans?
They’re going to use their parents’ devices, which are all age verified anyway.
More to the point: Age block technologies have been around since the mid 90’s and, for thirty years, parents have voted with their wallets and not installed them. In areas where they’re free, parents still don’t want them.