Actually...you've got it backwards. It's not the big clubs who insist on the co-ownership, it's the small ones.
See Borriello we gave him up for maybe 1 million(Total player worth= 2 mill). Suppose, he had been average. As in good for Genoa but not good enough for Milan, and we feel that's the best he can be. We can tell Genoa to buy him out, and Genoa will probably calculate that ok, his price on his performance would be now about 6 mill flat. But I already own half of him so to purchase his other half, I just need to pay 3 mill more.
Therefore Genoa end up paying a total of 3+1, i.e. 4 million for Borriello in total. While if he had been loaned with a purchase option, they would have had to pay whatever Milan wanted. So the big club is not bullying here. It's more power to the small guy. (IMG:
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Conversely, if he turned out good enough for Milan, we can get a player back. Someone who we thought wouldn't be too good, but turned out to be a surprise. Like Borriello! It's very rare to see, players who have been co-owned be brought back, unless they were really special. Because a co-ownership deal, unlike a loaning thing, can go on forever, till the player reaches his prime, and a decision is made once and for all.
And going from my earlier point of how it works out to be beneficial to the smaller club, this is exactly why clubs refuse to take great prospects from large clubs in Italy on loan. Loanees are almost always 2nd string players, who are meant to add depth. So a 4th choice player for Juve, might be loaned so he becomes 2nd choice at say Siena.
When both clubs realise they are talking a good prospect, the smaller club (fairly) plays hard ball.
'You're sending him here, to get him trained, to give him first team experience playing in the top level, and we have to pay his wages as well? What's in it for us?'
So if they buy half his contract, then that's it...they now have a vested interest, in developing him, coz now they know they can get him for cheap.
On the other hand, the EPL only has a loan with purchase option, which puts pressure. At the end of the year you have to say a yes or no as regards a purchase, when you want more time to check him out.
Yes, it works differently in EPL, when a player performing well in one season ,gives you enough cash due to a difference in table positions, but in Italy with TV revenues etc.. so low, for a smaller team, finish 9th or 13th doesn't make a huge difference in cash rewards. They need to gain something else.