Transformers as a series regardless of review scores and general has always been insanely profitable especially in foreign markets like China.
Despite being called the worst film in the series, Revenge of the fallen made $836,303,693 from a budget of 200million, this is an insane profit margin, especially since that 51.9% of the income, was from foreign film markets like China. Although the movies aren't making as much as they used to, it's still a very attractive profit margin for investors and the companies behind the movie. The Term you used gold mine would be spot on It's also interesting to see now how many Chinese Distribution logos are in the front of them movies. I know Age of Extinction had least 3. The Foreign market percentage has also increased tenfold, with 68.6% of a dark side of the moon coming from outside the US ( Over Half coming from Asia). For the latest film, that figure has increased even further to 77.8%.
Gold Mine For Hasbro Indeed