So if you’re designing an appliance that has to work with these two-prong outlets, especially if it has a metal housing, you want to know which wire is the “shock your customer” one and which is the “probably don’t shock the customer” one.
Everyone cares about polarity - when you have a 3 prong plug, then the ground forces the orientation of hot vs neutral, and the two prongs are the same size.
EU/German/Shuko and Italian plugs are entirely reversible and grounded, that’s what the OP probably was referring to. There’s no way to force an orientation (and thus a “polarity”)
Nowadays a lot of devices are made of plastic and / or are DC powered so it doesn’t matter as much.
What is it about weak eye sight that prevents someone from turning their plugs over when they find it doesn't fit the first time? Are people with weak eyesight also all THAT short of time as well?
Far easier with polarized NEMA plugs than, say, USB-A.
> I never understood why US uses a wider pin on two prong plugs
Because single-pole switches are cheaper, and ensuring the outer contact on an Edison light bulb screw fixture is neutral and NOT energized is an important safety feature.