This isn't true
The Flash has been the major DC release...for at least a year they've been showing trailers and advertising this movie. It has three trailers. It had a Super Bowl advertising, plus it has a TV show.
The writers strike just happen recently.
I'm NOT talking about the Flash specifically
But the strike and Ezra and the rest of the cast unable and unwilling to promote the movie did have an effect.
As well as every OTHER self inflicted hurdle the WB had to get over.
This movie much like Black Adam been in the machine for a long while.
There is going to be a book or documentary about all the behind the scenes.