They dont choose venue based on view lines lol. They choose them based on $'s. MCG+Vic Govt delivers millions more $'s than Accor. Simple economics
This is the simple reality of it all. Vic Government was prepared to pay more for the event, plus the NFL / LA had an additional 16,524 worth of inventory to sell at the MCG versus Accor. If the decision was about giving fans the best at venue experience, then it would have gone to Suncorp.
Melbourne also works well with the type of 'feel good' stories the NFL will want to roll out as part of the publicity tour. Things like
'the home of Australian football hosting American football',
'NFL being able to attract 100,000 people on the other side of the world' will all be wheeled out, as well as I'm sure something about the history of the ground.
That's not to say Sydney couldn't have had some feel good stories, etc, but commercially (which is ultimately what drove the decision), Melbourne added up.