-stand is what is (to something) or what has been established (about something). E.g., Bestand – the totality of what has been established about something, or what is available, etc. So Gegenstand is what has been established as real-world (or in extension also abstract) resistance to our objectives (so that we have to deal with it) – or, as gegen- is also vis-a-vis, what we are facing.

The Latin objectum has a directional vector (figuratively, it's thrown at us), while Gegenstand is much more inert. It's like a world view of active exploration versus a tableau of the world around us.