Top Bunk, I used to see the BA inhouse newspaper and there were regular letters along the lines of "airline A serves destination ABC and they're always full so why don't we?". To which the inevitable answser was along the lines of "We constantly review opportunities but we don't believe we can make money by serving that route".
Despite that, I reckon that you've made my point for me. The only way BA serve most of South America is through code share (remember LAN as well). There used to be enormous British investment in South America in mining, railways and who knows what else. We're still there; if I said "Antofagasta" would you think of the city or a UK PLC that runs mining and the FCAB railway in Chile, Bolivia and Peru to this day? I know that until recently I'd have said "city". Actually, I suspect many people would say a very basic "What?"! But that company is an exception.
In general, we (the British) and UK PLC seem to ignore South America. We hardly ever see news from the continent (other than anything related to the Falklands/Malvinas). I suspect most people couldn't even name more than 2 or 3 countries in South America.
On the other hand various airlines (not just THY) are opening routes into South America. There used to be only 1 flight across the South Atlantic (SAA) and now I think there are 3 or 4. Most European carriers (ignore TAP and Iberia for a moment) serve more cities than BA (for that matter Virgin doesn't go at all).
I simply think it's a shame that, as a country, we're missing out in so many ways. I accept that for BA the most effective way they have of serving the continent is by code share; we went LON/SAO/SCL using BA then LA and it was a very easy trip but I met a group that had come out on Iberia and they were saying "never again" so is it really good for BA if their flight number is on those flights?
Anyway, I had a great trip and I can reccomend Chile and Argentina as places that are well worth visiting.