Sharps and syndicates bet differently than an individual. They also get a lot more respect from books because they're typically known winning bettors...which is something not every book really wants to have as they are in the business of making money on games.
Sometimes they bet because they feel strongly about taking a position on one side of the game. However, other times they'll bet both sides in an attempt to middle the game and grind out a small profit. They might think "CLE should be priced at +138" and they'll drive down the price on them until they get down to below that point. Others might drive it even lower. At that point, they might be able to find CWS at -135 or lower. They can now have CLE at +140 and CWS at -135 and make a guaranteed profit.
Baseball is the one sport where if you can middle a game then you guarantee a profit. In games with point spreads, you look to get a 3-6 point gap where the game can land in the middle of the totals (say you have the Magic at +7 and Boston at -4.5 tonight and Boston wins by 5) and then you win 2 bets instead of 1.
Does that make sense?