Something wrong down t'cabbage patch

I bought the cabbage snapped left from a market stall this morning for 90p. A market stall which I might say gave far more space to exotic fruit and vegetables - no doubt some of which came from other parts of the European Union - than home grown staples like apples, cabbages and carrots. Tastes in such matters have clearly moved on in sixty years.

But the point of the post is that this cabbage cost the equivalent about 5 minutes work at a minimum wage of (say) £10 an hour.

In my capacity as a not very successful allotment holder, I very rarely managed a cabbage of this size and appearance, but if we suppose I managed to grow twenty such, I estimate that this growing would have occupied me for of the order of thirty hours, an hour and a half per cabbage. So what on earth do commercial growers do to get this down by a factor of getting on for 20? By even more if one allowed for the costs of packing, distribution and sale.

I leave aside questions of quality. My cabbage would probably be more organic, but would also likely come with a variety of unsightly livestock. Bought cabbages are apt to be much more clean and tidy - and apt, in consequence, to taste better, pride in production aside. Deadstock on the plate - that is to say boiled livestock - is surprisingly off-putting.

My estimate went as follows. Allow half a square yard for each cabbage, making 10 square yards, probably a strip one yard deep and 10 yards wide. Allow 10 hours for digging and ground preparation. Allow 20 hours for sowing, thinning, weeding and general maintenance. Including the provision of netting to keep the birds off the growing cabbages - netting which needs to be taken down and put up again every time one does a bit of work.

I did not use bought fertilizers so I allow nothing for materials.