Things are sometimes a little more complicated than that. It's not only the player's choice, but the selling club as well. Unless the release clause is met, both parties will have to be in agreement in relation to the club to which the transfer will happen. For example, during all his time here, Hulk raved about how he dreamed of playing in the Premiership. But no Premiership club offered (or would even come close to) the 60m that Zenit did, so his choice in the end was Zenit or Porto, the later most likely against the club's wishes and prone to make him feel unwelcome and some sort of financial problem at a club that needs to sell to keep the books balanced. Being a fan of the dude, I'm pretty much certain that his demeanor at the airport, when leaving for Zenit, wasn't the one of a happy man, but of a disappointed one. Of course, out of respect for his new club he had to keep the outward smile for appearances. Anyone who doesn't know this probably just labels him as another money-grabing thick dude that chose the Russian money instead of the chance at playing in a more competitive league.
I think players are slowly catching up to this. Jackson Martinez has so far cleverly rejected any renewal proposal that implies an astronomical release clause (which is already too high for a player of his caliber), in order to keep some bargaining power on his side during a future transfer.
Analogously, if Monaco is offering 35m to Sporting and they are sure the 2nd best offer (say, from a traditionally big club) won't surpass 25m or so, Sporting will do everything to push Carvalho towards Monaco.
And then, money isn't irrelevant in any one's life, let alone in the life of a player who's pursuing a challenging career that can go either way. We don't really know for certain what's the difference in hypothetical payouts. Would Moutinho preefer to be paid 8m/year at Monaco or 6m/year at United? Perhaps the later, but if the decision was between 8m and 2m it's a whole new ball game. In the case of Carvalho, and with the self-confidence that professional athletes necessarily have, I'm sure, if this came to happen, that he would be looking at Monaco like a stop-gap, confident that he can be playing for United, Real Madrid, or the likes, some 2 or 3 years down the line.
Then you have manipulative agents in which these players trust but that in reality will press them into the choice that will make their own pockets fatter instead of the one most likely to payout for the player (at all levels, monetary and competitive) in the long-run.
You're such a unique sort of spammer, Kevin.