Many of the huge transports that'll be coming to B5 were never meant to
operate within an atmosphere, they're strictly deep range starships, to which
you transfer using atmosphere-capable shuttles. We're not talking little
flits, we're talking about ships that can be as big as a mile across.
Dropping something that huge down into the gravity well of a planet is just
unworkable. If you want something that can handle lots of big ships, it *has*
to be in space...as in a station.
You could park a big ship near a planet, and use lots of shuttles to
unload it down to the planet (gravity well, heavy cargo, lots of fuel, lots of
time, more accidents), then haul it right back *up* again when it's sold or
transferred...or you could build a station in zero G where your big transport
just parks alongside, loads or unloads its cargo in zero gravity, and transfer
it where needed.
And the atmosphere of the planet is no longer breathable.