The Strait is one motivation, yes, but I was also talking more generally about the strategic balance in the region. Iran and Syria are the last countries in the region loosely aligned with Russia, and Iran is a major disruptive factor in the region. By destroying and occupying Iran like the US did with Iraq, in theory the majority of countries in the region would become subjugated by the US, hence long-term access to oil. Not that I think this strategy could ever work, but obviously similar thinking was also behind the Iraq invasion (in addition to the unfulfilled "promises" made by the CIA during the first Iraq war, which were a thorn in some of G.W.Bush's advisors).