Fans maybe, but we're not the target audience. We're only part of it, in a way larger pool of average moviegoers ! This trailer was to remind them "hey, Justice League is coming !", and it was just that, no real story points (other than the assemble the league point of course), noi villain, just leaguers in action. Same goes for the superman reveal, we've seen the set pics, the reports, etc, while most moviegoer do'nt go looking for that stuff. They may not now yet if and when he's coming back. They may even not have picked up the rising dust at the end of BvS...
Bigger picture guys, bigger picture. There are a lot of critics about the DCEU for different reasons, some really valid, some a lot more... trivial shall we say, but in the end remember that these films, while not having the success DC or we maybe wanted, still have an overall 66,6% approval rate and 3.7/5 score by the general public, and is making money for WB. It's far from the disaster some people try to present on the web !
And purely for comparison, Marvel has an average 82,8% approval rate with average score of 4/5. This tells me that the GA likes Marvel films better, probably because of a few factors, such as they were the first successful comic book franchise on the market, they cater their films better for the GA, and without a doubt, a strong leadership under Feige to make sure all the player stay inside their sandbox, plus probably dozens of factors I'm not thinking about. In my opinion, if DC wants to attain the same level of approval, they have to follow the same rules. Not copy the movies, but the organisation structure. Maybe have a story group, like Star Wars has now, sort of a supervising committee, that would be the equivalent of Feige, but composed of both filmmakers and comic book writers (and someone from WB, they find the money after all).