Yes, it's quite the mystery!
"Baby carriage" maybe ... but "baby cart" ... never!
I'd always assumed it was a literal translation from an uninformed non-native English speaker.
For this explanation to be plausible though, we need to find a language (or country) in
which "baby cart" is the idiomatic way to say "pram" - anyone know one?
Searching urban dictionary suggests
it might have been chosen for its lewd connotations - which is consistent with
the infamous goatse secret operator.
I think it's time to ask the BooK.