Interestingly, except for your first example, yours are all related to building or stacking things and returning to a fundamental, dare I say foundational, aspe

Interestingly, except for your first example, yours are all related to building or stacking things and returning to a fundamental, dare I say foundational, aspect. Also "being down" to do something likely came from writing your name down as a commitment, or putting a bet down, committing your money.