Sugar was Cuba’s main export for many decades and a big part of Cuban life in the 1970s was trying to increase the sugar harvest to pay off their debts to the Soviet Union see scene 19b
You can just call it ‘sugar’, or it can be quite a mechanical song focusing on the work required cutting the cane, gathering it, transporting it to the grinder etc. Or you could call it ’10 million tons’ reflecting the goal that Fidel set and the chorus could count up the tons and then stop at 7 million tons – which is what they actually achieved. The target was symbolically very important as it symbolised Cuba’s ability to stand on its own feet. Because of this there were many attempts by Fidel’s enemies (mostly US and Cuban exiles) to sabotage their attempts.