Mithrandir said:

This scene seems to be one of the post production made-in-hurry make ups. Or maybe it's a case of " what can I do with this awesome matte painting for which I've paid and I don't wanna leave unused". I mean, this isn't exactly the best example of ILM's work during its Gold Age

Well seeing how it's full of ILMers I would assume it was added late and shot at ILM, not at Elstree.

So maybe Lucas just thought the audience needed that little extra bit of info to show the transports that will be used and the dialogue about said transports.

it's a small bit but it does fill a gap in that we see a glimpse of the transports that are later referenced and it also adds some details about the evacuation underway.