Why not ? This is the only problem with the contract system, there is very little loyalty now towards clubs, especially if its not your hometown club.
You gave him a contract to play for your club for a certain length of time, if he completes that contract why should he not move on for better money if he can get it.
There is always the Player-go-round stories before the end of season, of who is going where. It is also happenning with coaches now, Nathan Brown going to St Helens, How good is that for the club, players and fans of Huddersfield ?
Contract talks for players and coaches should only be allowed to be conducted and announced in the close season.