The average commute in the US is 50 Km per day and if that is the average it is reasonable to assume some communities will be highly correlated above average, for example if they are 40-50 Km away from a large economic hub, a large proportion of residents will drive the 100Km roundtrip per working day. The lower price of electric comute will prompt many residences to have two electric cars driving the average every working day, for a total, again, of 100Km = 20KWh. So double digit is not exceptional, it will be the average, an extra 3KW of power for each household for the entire night, assuming an outstandingly smart grid that can perfectly level off demand.
Combine that with rare events like hot nights and large movements, psychological reactions like panic, and you have an unreliable local supply that might trip every few months without expensive upgrades.
There is plenty of capacity available, provided charging is spread out over the night and not concentrated at peak demand periods. You just need chargers that are smart enough to ensure this happens.
But that doesn't mean everybody in your neighborhood can draw 24KW all night long. Those are maximal currents for intermittent loads like heaters, clothes driers etc. You might have a single 100KVA polemount transformer suppling a whole street and a single 15KV / 300Amp line servicing a whole neighborhood.
When everybody attempts to draw even 5-10KW in the air-conditioning season, you get circuit breaks because the main feed is incapable of supplying sufficient power. The upgrading will be done but it will take a decade or more, especially considering the push from local municipalities towards buried power feeds which are very expensive.