A club could go out and sign a magnificent player. But if the style of football in the SPL just doesn't suit their style, they're nae exactly going to be at their best. For example, a player who prefers a bit of time on the ball to work some trickery and nice wee flicks and touches ain't gonna like the traditionally lightning-fast pace of the SPL. Let's face it, the SPL has never really been the best breeding ground for skill.
If a player has already played, and played to a reasonably successful level, in the SPL, it's gonna be less of a gamble for the club to sign him cos they already know he can cope with the physical demands of the league