Why would someone join the Army or Marines over other branches?

I know this may sound like a stupid question, and I have a ton of respect for the Army and Marines. But given that we're involved mostly in land-based guerilla wars, why would most people choose to join the Army or Marines rather than a branch that would involve less risk of physical and psychological trauma. Now, I know many wish to serve their country in active combat, which would make the Army the logical choice. But many I've met just want good career skills and money for college. So why not just join the coast guard or the Navy? Not that those guys aren't tough too.