I have elementary school age kids, so I know lots of parents. Anecdotally, there is a
big jump between having two kids and having more than two. I've had a lot of conversations with friends on their third pregnancy about having to upgrade to a bigger car because with the size of car seats, you can't fit three of them in one row of a typical sedan. And I've likewise had conversations with parents who decided (like my wife and I did) to stop at two, and many of the reasons are fundamentally about logistics and resources. Transportation is a real component of that.
If you take a step back, it does make sense. The difference between zero kids and one is a major qualititative lifestyle change. It's the transition from parent to non-parent. It means not easily going out at night, schooling, etc. Everything changes.
The transition from one to two kids is a qualitative change for the kid because it means going from no siblings to siblings. That transitively makes it somewhat of a qualitative change for parents. It means the kids always have a playmate and someone their age on vacations. But for parents, it's mostly a change in degree. More work, more cost, more time parenting, but the overall lifestyle is basically unchanged.
The transition from two to three is really just quantitative. 33% more space in the house for sleeping, 33% more food costs, 33% more car space for transportation, etc. So the decision about when to stop is mostly just "how much of this experience do you want?" The transportation overhead here in the US where you do a lot of driving is a pretty big piece of that.