The points awarded per unit distance isn’t quite equal.
20 points / km is greater than 30 points / mile. The difference being ~7%.
As a UK rider I tend to prefer imperial but can’t help think I’m being short changed lol. I realise it’s not a big deal but as people’s Zwift mileage grows the delta will only get bigger.
Maybe the points could just tick up one at a time every 50m regardless of unit choice, when it’s ticking up so regularly i don’t think the imperial users would mind that it’s not at ‘round’ intervals.