International competitions is not as attractive as domestic leagues including World Cup but of course it is all about preferences.
I think the exposure of players in an international competition depends on how well they promote the event. If the event is well advertised then the curiosity of viewers will be triggered. Aside from that, they probably failed to set a match-up comparison of ace players of different teams and create a sense of rivalry between them.
I believe there are many gamblers who like to gamble on International competitions because they know how to maximize the chance from the matches. Some people may think that predicting international matches is easier than domestic league but some other may say the opposite.
The complexity of predicting winners depends on how well the bettor knows about the team composition. I think there is no difference between domestic and international betting difficulty as long as we know the skills of all the players involved.