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.

jms