Since planets are so huge, wouldn't it make more sense to send a number of different away teams down - one per continent at least?
That'd kind of highlight how interesting stuff only happens to the people whose actors are named in the opening credits, wouldn't it?
(But yeah, it would be a nice touch to at least mention that there are other landing parties, even if they don't get to see the interesting stuff, at least on missions like explorations of uninhabited worlds where in principle the worst anyone can get is killed by the naturally-occurring land mines or whatnot.)
They did once mention other 'away teams' in an episode in TNG. I can't remember its name though. I think they were looking for something...
Of course all we saw were the main actors.