for bridges its simple. once all players leave that map, the instance no longer exists, which means when you log back in, there is no where to put you, so it defaults to the "last active map" you have been to, which would be sector or system space depending on where you went tot he bridge.
for fleet bases, i think its so non-fleet members that are invited to the base dont get stuck there when they log out.
I have a theory that starbase systems are built on the same mechanics as bridges. Think about it:
If you beam to your bridge, or transwarp to your starbase sector, when you leave you return to where you came from.
If you log off there, you return to whichever map you were on previously.
If you're in the starbase system, you can't visit your bridge.
They both have several decks/floors, with just one way to go between them (turbolift). You can't even return to starbase sector space from inside the starbase without using the turbolift.
Comments
for fleet bases, i think its so non-fleet members that are invited to the base dont get stuck there when they log out.
If you beam to your bridge, or transwarp to your starbase sector, when you leave you return to where you came from.
If you log off there, you return to whichever map you were on previously.
If you're in the starbase system, you can't visit your bridge.
They both have several decks/floors, with just one way to go between them (turbolift). You can't even return to starbase sector space from inside the starbase without using the turbolift.