This is caused by three things; A series of reductions in force that always cuts more enlisted than officer spaces , thus nudging the ratio down a bit with each iteration. A strong desire for an adequate mobilization base of officers, particularly Flag Officers leads to a padding of officer strength -- most of the excess is simply parked on too large staffs at all levels, the ratio of officers in contact with or command of troops hasn't changed much. The third factor is the Statutory requirements for fairness and equity in promotions. Congress demands an equal shot and the up or out process required to satisfy them entail a very wide pyramid. There are many other factors but those are the big three. One minor factor is the dumbing down of the US educational system at the secondary level for a number of reasons that result in a belief that a college degree is required for anyone who must think. Yet, as MattM said above:
Currently, all services accept a degree as a qualification that one can obtain a commission; and the process requires very little evidence that an education has taken place.
I figure if we keep playing with the uniform, giving out high level meritorious service (as opposed to combat) awards to people for just doing their jobs (Someone senior note a LTC friend of mine had seven Meritorious Service Medals and asked him why. His reply: "I PCSed a lot" -- meaning that he got one every time he transferred) and the Officer to troop ratio keeps going down, we'll resemble one of those Armies that we used to make fun of...