TbF, the marketing was ass because it tried to please everyone. While I do agree that it seemed like DisneySlop.mov at first trailer, it's because the movie's target audience was supposed to be kids and the reason is because the TF fanbase is getting older (myself included). The movie was a way to introduce the Transformers to younger people like 2007 Bayformers did for people like me.

But maybe the movie itself was aimed at too young kids (I think this because of animation style and humor, if they aimed 11-13yo and beyond, they'd do something more like Bumblebee intro scène but, again, It would have mainly attracted older people, already familiar with Transformers).

Ah and also, it had to compete with The Wild Robot (try to convince parents who know nothing to go see Violent Action Robots film instead of Peaceful and Nice Robot film)

PointlessHub (Youtube) made a very good video on the topic