I mean that everyone can have a bad night. Just one fight with poor performances did not mean that everything is done.
I thought Jacobs was bigger and better than anybody thought he'd be and Golovkin still beat him convincingly. I think Jacobs would stylistically be a bigger problem for Canelo than even Golovkin and that he'd light his ass up. People think Canelo beats GGG for the following reasons: 1) GGG / Jacobs, where Gena didn't blast DJ out like everybody else 2) They're delusional 3) Canelo has youth on his side 4) They're delusional 5) Canelo has gotten dodgy scores from judges before and he's a pretty tough guy. If he makes it to the end he might just get a very favourable scorecard. 6) They're delusional.
I believe for a big percentage it's actually more hope as believe. The Jacobs fight probably has fueled that hope, but be fair here, the dominant #1 160 should always be the favorite over a big name guy that never even fought at the weight.
7) Floyd and Ward fans masquerading as Canelo supporters, who are desperate in hope, to see the very man who made their heroes cower away, fail
Because Canelo is a good fighter. Regardless of how he acted during making this fight, both are great fighters. Canelo has the speed and slick defence to box & counter GGG all night and that's how he wins. GGG's power once looked absolutely unbearable, (Although it is still the top in MW and probably weights around him) however I think Jacobs and Brook showed that people can take the shots on the chin (Obviously it broke brook's eye socket, but he took the shots). If Canelo gets into a fight with GGG and brawls, GGG will win.