They're public access. Nursery ryhmes and songs don't belong to a particular artist or creator because they're essentially folk songs/lore or old Timey sayings that got put to a handy jingle while you work the day away. or rooted in it at least. So. That means they have a guaranteed likable child song that's no effort to create, and completely free and has no risk of infringement issues or suites. It's primarily laziness in my opinion. I also think some of the more innocent content(in this case music accompaniment) is placed throughout as a diagractor. Parent looks over or listens in more closely from the drivers seat or other room and just hears some innocent inane child's song. Same for the more normal animations leasing up to some weird or inappropriate stuff