There are tons of reasons to trade a player. Sometimes the offer is just too good. Sometimes room has to be made for another player. Sometimes the team just plain has needs and it just has to be done. That is baseball and that is just how it goes.
So with all that understood, please do not trade Tommy Pham, Cardinals. Not because he was the brightest spot in a frustrating 2017 season. Not because his contract is a bargain at four years of team control - one at league minimum and three arbitration years.