Long contracts are usually described as commitment or as protection against poaching. The stronger explanation sits in how a transfer fee appears in a club's accounts.
A fee is treated as an asset, not an expense
A signing is recorded as an intangible asset because the club has acquired the right to a player's registration. The cost is then written down across the period that right lasts.
That period is the contract length, so the annual charge is the fee divided by the number of years agreed. Nothing about the cash payment schedule changes this.
The accounting charge and the cash outflow are separate things, and they frequently move in opposite directions.
Longer contracts reduce the annual charge
Spreading the same fee across more years lowers the amount recognised in each set of accounts. A club under a spending control measured on annual figures gains room by extending the term.
This is why unusually long deals appeared in clusters after financial regulations tightened, and why governing bodies subsequently capped the period over which a fee may be spread.
The cap exists because the incentive was working exactly as anyone would predict.
Wages behave completely differently
Salary is an expense in the year it is paid and cannot be spread. A long contract therefore commits a club to a fixed annual cost with no accounting flexibility attached.
That asymmetry means length reduces the effective cost of the fee while increasing exposure to the wage. The two effects pull against each other.
Clubs manage the tension with performance-related pay and appearance clauses that shift part of the salary into a variable band.
Selling reveals the accounting position
When a player is sold, the profit recorded is the sale price minus whatever value remains unwritten. A player near the end of a long contract has a low remaining value and generates large accounting profit.
Academy graduates carry no acquisition cost at all, so any sale is almost entirely profit. This is why homegrown sales are disproportionately valuable to clubs under spending pressure.
Understanding this makes several otherwise puzzling sales legible as balance sheet decisions.
The model breaks when players decline early
If a player loses his place, the club still carries the remaining value and must eventually recognise a loss. Long contracts increase both the size and the duration of that exposure.
An unwanted player on a long deal is close to unsellable, since any buyer inherits the salary while the seller resists a loss.
The stalemates that produce players training alone are usually accounting problems presented as disciplinary ones.