TROS only made a billion because it was more of a sequel to TFA than TLJ and it had palpatine and the finale effect had a positive impact as well.

If it doubled down on TLJ’s story direction or refused to bring back palpatine or was part 1 in a two parter…or god forbid all three…than I would not be surprised if it struggled to make justice league numbers(600 million)

Don’t underestimate how many people loathed the direction that TLJ was going in and how TROS was lucky to make the money it did