I think the more limited coaching time with intl football perhaps makes it more worthwhile to focus on a defensive system.
I'm obviously not a coach but if I had to guess, training lots of attacking variations and positioning is probably a slower and more complicated process than training your defensive shape and marking scheme for whoever your next opponent is. So if you're trying to get the most out of a group of players with a limited familiarity in only a couple of weeks of training, you probably get more out of your time by focusing on defensive preparation, even if it means leaving your players largely to work it out themselves creatively.
This is probably why it's also a big advantage to have players who are used to playing with each other, and to have a kind of philosophy instilled and maintained in the national team like with Germany, Spain and Chile in their tournament wins.
With club football there's just so much more time that at a certain point continual defensive coaching is going to bring you more and more limited returns. You can only drill a team into its shape so well. At a certain point you have to move on to working on how your team attacks, and developing a deeper kind of understanding than just picking the players and sending them out, and hoping your training gets a clean sheet and the players get a goal.