You really think that the direct sequel to BvS and the fact that BvS let many people down had no effect? Transformers were never known for their quality and the box office recipts finally caught up to match the quality of the film.
People were burned out and everyone was cautious because they didn't want to be let down again. Thats why JL's hype levels weren't as big as Thor Ragnarok. And when the reviews came in and social media generally said it wasn't bad and it was just meh, it was the final nail for those on the fence of watching the film.
But its not the end all be all factor, marketing wasn't as engaging as SS or BvS. To deny BvS' impact is just foolish. I saw so many comments online and heard in real life people being "cautious" and waiting till reviews came in or a friends review of the film before they saw it. But again, its not the end all be all factor.