Because it’s not a good idea, everyone else becomes inconvenienced and/or subject to spyware just to arbitrarily age-limit something that doesn’t have to be age limited, and despite that inconvenience, it will inevitably be worked around by motivated 13 year olds.
> to arbitrarily age-limit something that doesn’t have to be age limited
There is evidence of a growing consensus that this does have to be age limited. Both in the research and in voter polls. (I personally believe in it.)
> it will inevitably be worked around by motivated 13 year olds
The same goes for liquor and cigarette laws. They're still of net benefit.