Co-productions mean TV dramas produced by production companies from Taiwan or Hong Kong together with a mainland TV station. There is no cap on the number of dramas a company can produce, but they cannot get a prime-time spot on any station. You would be producing with prime-time costs only to be put in a second-choice slot, which just doesn't pay.
「合拍劇」則由台港製作單位與大陸電視台合拍，沒有名額限制，但不得登上任何電視台的黃金時段，形同以黃金檔成本製作二線檔期，很不划算。