Perhaps they have priced the 5sp artificially low to advertise some price, not intending to sell very many cars so equipped.
So they lose more money on a manual so they can put an ad in the car magazines that says the Astra is $14995 (or whatever it is, just throwing a number out there.)
But they don't make very many, as most of them are the automatics and are over $16K (using my contrived example)
That's just speculation, it's worth very little, if anything.