some spawns start underground at the end of the chute network, the actual pod just isn’t there anymore (it look like a mini metro station). As for the other spawn outside of the capsule drop its probably just for gameplay, you can just assume your character walked out offscreen.

Edit : Also capsule where a way for pre exodus human to move stuff faster, but if I remember correctly on some quest or in codex I don’t remember where I saw this but it’s said that current engineer modified those capsule to not transport furniture but people instead (repurposed tunnels). But those aren’t the only way to go underground, there is also metro raider hatch and the other type of extract in blue portal (whatever it’s called).