I can speculate on the popularity of delta voltages in US distribution, but only with personal, anecdotal correlation. Probably some tendency towards delta secondaries in utility distribution grew with the practices of system grounding and related codes that grew more common, which was a passionate issue in the early 20th century. A breakpoint of sorts in AC electrical-history accounts seems to be 150 volts. The ‘habit’ seems to be, if low-voltage service entrance could be grounded to keep conductors under 150 volts to ground—it was, where if greater than 150 volts, grounding was optional with various arguments for the acceptability of the two practices.
Another small difference has been the tendency for 2:1 voltage ratios {for transformers and motors} in the US, corresponding to dual/split/tapped windings, versus 1.732:1 ratios popular in other areas, corresponding to phase-to-phase and phase-to-neutral voltage inherent in wye windings.
Habits are hard to break, but a classic power-systems text [Beeman’s Industrial Power Systems Handbook] has advocated the use of 208Y/120- and 480Y/277-volt systems since 1955.
