There are probably a variety of reasons.
First, a couple points from the ISO 11540 document preview that you can get without shelling out nearly $70...
"It relates to such instruments which in normal or foreseeable circumstances are likely to be used by children up to the age of 14 years."
"It is, however, acknowledged that certain products (i.e. writing and marking instruments which are designed or only intended for use by adults, e.g. jewellery pens, expensive fountain pens, professional technical pens) are not intended for use by children and such items have to be clearly labelled to that effect."
Also, just because there's a standard doesn't necessarily mean that companies are obligated to follow them. Out of all the other fountain pens I have (Pilot, Lamy, TWSBI, Kaweco, Conklin, Monteverde, Noodler's) none of them have a breather hole like the one on the Parker Urban. It would have been nice if Parker could have found a way to have the breather hole a little further down on the cap body so the inner cap could remain intact and properly seal the nib.