I can't tell you why that is in general, but I can talk about the specific case of why I did for the bike bus. I could see a similar benefit for adults too (like a casual bike-pool), but adults can go directly from A to B at their own pace, and leave at their own time, they have disparate workplaces, can better mind their own safety and be more visible on the road than kids. So the bike bus I see as way more beneficial for kids getting to school, than for adults going to work or other places.

Interesting point, I would probably do the same without thinking. I guess as a parent the most important thing to me is my children and to improve the world for all children so it's better than it is/was for me. They don't have a voice, don't have a voice and don't really have a choice of transport like adults do so this could be more impactful for them than any other group. Yes of course it'll help adults too and that is important. It's just such a natural thing to say without thinking