I do believe it is to allow each hotel (or MVCI property) to have the flexibility of not listing certain room types or to allow for multiple upgrade instruments (i.e. 5K awards or cash).

Note that I do believe that normally, the online reservation system will show the "total" number of points required for a particular room. For example, I just searched for an MVCI property that has studios, 1, 2 and 3 bedroom units. A studio unit lists for 120K points for 4 nights. A 3 bedroom unit shows up as 180K points. (And the Rate details shows that the costs is 120K for a base room plus 3 upgrade certs per night or 60K for upgrades which means a total cost of 180K.)

Also know that a number of hotels may not put all their "upgradeable" rooms in the online inventory. Thus one would have to call the hotel to see if they would offer those room types for awards and if so, how many upgrade certs 'per night' it would cost.