[zamadatix]

A wired connection to a house in the US usually only supports a single IP to be shared by everyone in the house. Kids also access the internet from more than their home (e.g. libraries), so this also runs into overlap elsewhere too.

[dTal]

Mobile phones rather famously tend not to be plugged into landlines.

[nancyminusone]

not with ipv6

[zamadatix]

That's the unusual part (for wired connections in the US at least) and it's story isn't much better, it just didn't make much sense to detail its "why"s when the usual part (IPv4) already doesn't work for much simpler reasons.