Its the signing on fees that empty's the bank balance. If there was a 5 year option you would offer it to 18/19 yr olds. If you "power train" them signing a new deal every 3 years gets too expensive (unless you're a token buyer).

Some people will agree with 5 years some are happy with how it is now, so at least have the option of how many years the player gets. (And maybe negotiate with the signing on fees).