In addition to zck's points: obj is built using listtab, and there's several cases in arc where 'internal' helpers are not distinguished from the external interface. That gives users the option to use it in the rare situations where it's more helpful.
Also, it looks like you're new here. Welcome! Feel free to post any questions or thoughts about Arc; this forum is really welcoming to newcomers, and I'd like the community to grow bigger.