> but doesn't really affect society very much.

In addition to the items you mention, there is an embodied carbon / pollution component to manufacturing these barely used second vehicles.

That's fair. Although it's partially (mostly?) offset by the preferred solution here of using Uber, which produces tons of extra CO2 from cars idling/driving around waiting for a fare and driving without a passenger to pick you up.

I'm not saying getting rid of these second vehicles is bad, it's great, but Uber's specific focus on rarely-used vehicles only makes sense because they want to make money. Any independent observer concerned about CO2 or pollution or traffic or road safety would want to incentivize getting rid of cars in general, and put more effort towards frequently-used cars.

Taking kids to weekend sport in Australia is not a one-off occasion. It's every Saturday morning. It produces its own peak hour (approx 10am-1pm Sat), focused in certain suburban areas, that's often worse than weekday peak hour in the city centre. It's also really hard to do it without a car. The sport locations can be quite unpredictable (sometimes in your local neighbourhood, sometimes a 2+ hour drive away). They're seldom accessible by public transport. And (in Sydney at least) children under 7 need to be in a car seat in an Uber (but not required in a taxi!), and no Ubers with car seats are available. So it's not only much easier, but also probably fairly cost effective in the long term, to have a second car with 95% of its use being for weekend kids sport.

Right, but having to use your second car for that trip and only that trip is probably a rare occasion for many families. I imagine the most common cases are two cars that are both used regularly because both parents drive to work, or one primary car that can be used both during the week and for that Saturday morning trip, and the second only for the rare occasion that the primary car is broken or being used for something else.

My point is not that nobody needs a second car, my point is that focusing on rarely-used cars is by definition not a major societal issue. What you're describing is a very real issue, and might be more appropriately addressed by improving public transit. Uber's idea of replacing your second car with ridesharing does not work, as you say.

Edit: Also note "most of them are in two-person households." So it seems they're mostly focused on couples without kids.