Many of them actually are.
The best ones understand that their clients development needs come through playing time at whatever level the player is best suited to.
Not through training and playing for U-nderage squads on big clubs where an immediate breakthrough to the top squad is unlikely. No agent wants to see a client flounder at a big club and have to be sold/loaned out to some lower rated club, especially in a league that isn't in France, Italy, Spain or Germany.
What gets fans pizssed off is when a player egotistically ignores that advice or when a club simply throws too much money to say no to at a player they want to keep away from a rival club. Agents are advisers, not controllers.