The reasoning is simple, Marc Rubio holds a grudge against the anti-conservative forces throughout South America. This likely grudge comes from his parents and Miami Cuban conservative community (they are all big on South American regime change). It also happens to coincide that oil corporations want to sell more of the oil on the global market.

If you want to learn more about the why, I suggest the book "Gangsters of Capitalism" by Jonathan M. Katz it's about the military exploits of Smedley Butler and how they helped American imperialism.