There are very few countries where voting is mandatory, perhaps none. And still The USA has lower voter turnout than most, probably more because of the separate

There are very few countries where voting is mandatory, perhaps none. And still The USA has lower voter turnout than most, probably more because of the separate registration step than anything else. But the biggest difference is the per-state first pas the post mechanism, which is what creates the phenomenon of "swing states" where relatively few voter decide everything, and almost any expense of effort by campaigns is worthwhile.