Hi there. To put it short, all those people are playing with the original Rome game and not the expansion, BI. You can only play BI in multiplayer against another BI user, and since these are few and far in between, you will unfortunately have a hard time finding a game. As Ludens briefly hinted at, the unfortunate truth here is that CA, in developing the Rome series, did not integrate the expansions within the original, hence segregating the individual expansions from the original with regard both to single and multiplayer modes.