CFL is an unique league where good players are often released or traded for almost nothing. In other sport leagues, transactions are costly or trades appear to be for roughly equal value. Perhaps, oversupply of American football players result in easy replacements?
Not to be picky, but nobody ever gets anything when they release a play=yer, in any league; but I know what you mean. In the CFL players who could still play on the team are often released to give the NFL a shot. I expect it is to maintain a good relationship with the player/agent should that player ever return to the CFL.
As for the quantity of import talent, that is absolutely a factor (IMO). What further complicates trades is if an Canadian is involved. As well al know, with players of relatively equal talent/performance/age/etc. a Canadian is more valuable.