Why would Jesus Christ ascend, then descend again?

Millenialism , as such, postulates the return of Jesus Christ to *this present earth* to reign for a thousand, literal, years. The evidence for this is taken from the visionary mention in Revelation. This view has serious Gospel implications regarding an earthly reign and regarding the concept (held by some) of the re-instating of sacrifices on earth. The article to which I have linked, explains various historic forms of this doctrine. Anti-Millenialism states that resurrected saints and saints remaining on earth, will be *caught up* from this present earth to Jesus Christ and there shall be new heavens and a new earth (once Judgment is effected). They say that the thousand years in Revelation is a symbolic figure and relates to the present rule of Christ over deceased saints in heaven and faithful saints on earth, in a reign of Spirit, not physical. Importantly, and importantly to my present question, they say that Jesus Christ *shall never set foot, again, on this present earth.* There are implications to Jesus Christ returning to earth for a thousand years and re-instating an *earthly reign* : implications regarding the parables of Jesus, which express an immediacy and urgency regarding an *everlasting Kingdom*; and implications regarding the apostolic epistles which, again, express immediacy and urgency regarding a *finality* associated, immediately, with the return of Jesus Christ. My question is, Why did Jesus Christ ascend, if only to descend again, thereafter, in order to establish an earthly kingdom ? Why ascend at all ? Why not remain and reign on earth ? What do those say who adhere to the Millenial system ?