But that's because you only focus at their value when looking at the prices, there are other factors. When we bought Zaza for 3.5M we also had Gabbiadini and Immobile all on coown and one of them was supposed to come here one day, we didn't know which one yet, but all were out to prove themselves. Ciro managed a great season but was "sacrificed" for Morata, he also didnt want to come here, so we were left with Zaza and Gabbia. We rated Zaza more but didnt need him in 2014 as we had Morata, Tevez, Llorente, Giovinco, Coman and werent as good financially because of EL so we sold his half for 7.5M (a fee Sassuolo would never pay if we didn't guarantee to buy him back) to recover some money after paying 20M on Morata. Sassuolo basically did us a favor which we repayed a year later. Zaza was an Italy starter and came of a season where he scored 11 goals at the age of 24, we didnt overpay that much if at all, all things considered.
We tried the same with Berardi, he was supposed to come here but refused, we still have rights on him though and will buy him next summer most likely.