Answer: because they're clueless. Every single day there are players or teams opening as dogs and closing as favs just because of the flow of money. Even the mighty Pinnacle sometimes opens a market and the price moves significantly within the first hour. Like when Fognini opened at 2.45 vs Zverev and people pounded him into favorite at 1.87. If the books can't price the 4th round of a goddamn grandslam correctly and be off by a mile, that's proof the odds makers are prone to huge mistakes, and so is the market.