Obviously the voltage difference alone does not itself explain the reason why an e-GMP car like the ioniq can charge in 20 minutes rather than the 30 a model 3 takes, but there are very clear economic advantages to going with high voltages rather than high current.

Because the limit is, in a real world practical sense, in the charging cable. An 800V fast charger can ramp to higher power levels much more cheaply than a 400V high current charger for all the same reasons the cars benefit from 800V. less metal or cooling/station = more stations (ceteris paribus)