The Saints are getting a generous amont of points against a mediocre Seahawks squad because Drew Brees is out. Teddy Bridgewater, though, is one of the better backups in the league. Bridgewater gives the Saints a running dimension from the quarterback spot they lacked from Brees. He has excellent weapons with Alvin Kamara and Michael Thomas being among the best at their respective positions. Offensive mastermind Seay Payton can also coach Bridgewater up with a full week to prepare.
The Seahawks were outgained by nearly 200 yards at home by the winless Bengals in Week 1, lucky to escape with a victory. Seattle then caught a break this past Sunday against the Steelers when Ben Roethilsberger couldn't go in the second due to an elbow injury. 
Seattle's home field isn't as dominant as before and the Legion of Boom is no more. Instead the Seahawks have an inexperienced and vulnerable secondary.