Understand. My bet is that if they stuck with their original plans they would slowly grow an audience sizeable enough to be profitable.
Cinema is expensive ($16.50 per ticket, $20 for drink & popcorn where I live). It takes a lot of convincing to get me into a theater seat! One way of doing that is building momentum. Sure Transformers didn't do too hot at first (crazy $129 million isn't successful), but there's a lot of friction involved thanks to franchise fatigue, "Disney humor" fatigue, and uncertainty on what age demographic it was for. The trailer would be the place to address all of this, but it instead it did the opposite (and wow, the spoilers), and worked to create even more friction.
I think now enough people have seen it and no longer have those concerns a sequel would be a much easier sell.
It makes me wonder if maybe we have the theatre model backwards. First limited streaming (with discount) -> theatrical release if popular enough (more expensive to stream now) -> physical release with extra goodies.