Why on earth wouldn't you just tell the kid to walk several blocks, and then meet them there 10 min after school ends or w/e? Maybe not practical for younger elementary aged kids, but definitely for middle schoolers.
Because the school (encompasses K-12) was built in front of an industrial park and is located along a major highway. The kids are not allowed to walk off campus for safety reasons. They have to either be picked up by a parent or bused home. The school is not located inside a neighborhood. The whole first year after it was opened the lines were horrifically long and the kids had nowhere to wait except outside in direct sunlight (100 degree heat at times) because the pick up location was not directly in front of the school because that was where the buses were loading (very poorly thought out drop off/pick up lay out). Parents pitched a fit. They finally created a covered area so the kids would have some shade. The next year they started staggering the release times, which did help some.
When I lived in Omaha NB, I walked to and from school as a 1st grader/2nd grader, sometimes in huge snow drifts. I don't remember a pick up line but I was never picked up so maybe I just didn't see it. I lived several blocks from home but walking was what nearly every kid in our neighborhood did. We all walked together. Same with 3rd grade in Abilene TX. The kids walked if they lived close enough (meaning a few blocks). I don't remember pick up lines there, either, but again since I didn't get picked up I may just not have noticed.
5th grade there were definitely pick up lines (5th grade San Antonio, TX). The school was not located in a neighborhood and there were no sidewalks. Some industrial, some commercial, some empty fields. Most parents picked their kids up or had them ride the bus. I don't know of a single kid that walked. I do remember seeing the cars in line to get kids. No idea how long it took. I rode the bus since my house was a loooooonnnnngggg way from the school. Definitely not walking distance unless I wanted to get home well after dinner time and again there were no sidewalks along the way so I would have been walking along major roads.
It does seem weird to me that there are these long lines but I think maybe in some areas there have probably always been lines. I think it is more likely today though (although I don't guarantee that and I can't say for sure why I think that). As for the why, maybe there are a lot of schools being built that are not right in neighborhoods perhaps? Or the policy has changed on allowing kids to walk? There have been other reasons mentioned up thread, too. I wish there were a reliable source that had data on this. Now I'm interested...
The elementary school around the corner from us has long lines now. It is a nightmare trying to get through if I have to go that direction because there is this massive line of cars weaving through our neighborhood. Parents are trying to pick up their kids. I'm wondering if school policy changed and they are no longer allowing kids to walk home. This school is definitely inside a neighborhood and if they were willing/able to walk a couple of blocks the parents could pick their kids up without waiting in line. I do know that parents are not allowed to go inside the school to pick up their child or even use the restroom during pick-up/drop off. You have to remain in your car and a school employee will put the child in your car. There is busing but only for kids that are outside the 2 mile line.