Agreed, the earlier movies were a mixed bag but since they were marketed as existing in one universe and were leading upto some big event movie (JL) like MCU movies do, people showed-up to watch them in theaters, respective of their RT ratings. Earlier DCEU movies got commercial success but couldn't get critical success (for most part)
Now, they have said that we are focusing on movies as stand-alone entities, so people are not thinking that these are "must see" movies which has resulted in critical success but commercial success is a mixed bag. In a way, it's opposite to what was happening earlier.
The solution is simple, just have a plan to build towards some crossover-movie (they don't have to announce the actual release date for it) and make movies connect loosely, perhaps a after credits scenes from next movie ? Which will get more people interested.