What surprises me about the Clark transfer situation , is that he signed a 4 year deal only at the end of last season, if he wanted to get away surely he shouldnt have signed a deal with Cas.
TBH, the way I see contracts really is a 'win win' situation for the player. The club themselves use it as a marketing tool to say Player A has pledged their future to the club etc etc. But in reality it offers the player security of his playing conditions and pay, but for the club it would do little more that add some security of being paid out if another club wanted to buy a player whilst still under an active contract.
So in terms of why would Clark sign a long contract and then request a transfer so early into the contract??...Well why not? The player has nothing to lose, and potentially many things to gain! Forget about the loyalty side of things, sadly loyalty barely exists in today's game at any level.