Damocles said:
And if they would have waited a little longer they would have gotten him for nothing, hence the value of a player is at its height when a contract is signed and loses value every single day eventually reaching zero on the last day of his contract where he can move for free.
Of course.
But that rather simple explanation completely ignores the fact that a player's worth is also driven by how good he is and what his potential is. Sometimes those factors MASSIVELY outweigh the mechanism you describe, as my example shows.
So to say all our players are worth less than 1 year ago, simply because their contracts are 1 year nearer to renewal is plainly bollocks. David Silva has less time left now on his contract compared to when he joined, but is certainly worth more than had we sold him back then.