Laziness... sure, its a port, with a tweaked engine. Do you have any idea how much of a chore it is to make links for 82,000+ code shortcuts, and then test each one to make sure that it still links to the correct thing?
For example, The shortcut code for a specific item, may point to a line of code that exists at BE22 60FF, if you tell the engine to use that address, it will have the correct values. If for example this is Cale's Helmet, and you upgrade it from +2 to +3, the code will then shift to BE22 61FF, which links to the stats stored for the +3. When adding this item to the game, it creates a minimum of 3 separate addresses. The items visual information, its physical attributes, and its location/status. If the item is dropped, it has another location, adding shopkeepers, a gifting system, etc all add new links that need to be programmed to link to that item.
Rather than sifting through the code to find these links, it is re-compiled.
Trust that FROM knows the game has to launch in a specific window to be successful as a PORTED upgrade. a Simple, Hey you can't import your characters warning, simply tells me, the game will release on time, and not 2 years from now, because of character imports.