The 1mb is not part of original design. Increasing the block-size is.
If arbitrarily increasing the size without regard to external considerations was the "design" it would have been preprogramed to do it automatically, just as it decreases the subsidy automatically, or controls difficulty automatically. Try again.
Wasn't the 1MB cap just a quickie kludge at the time when blocks never got that big, sort of a "if it's 1Meg, 100% chance of it being spam," erring on the permissive/high side?