There are several possible reasons:
1) They are putting an end to people fornicating with their orders to seek an advantage.
2) They build cars in batches, or production runs, rather than order massive amounts of everything and warehouse stock they decide what will comprise the next run order parts for that. Some parts/sub assm come in fast, some slower so the slower items are ordered in advance so they will arrive conterminously with the other items required for a production run. By people fornicating with their orders it reeks havoc with their production management, thereby negatively effecting everybody.
3) We aren't there. They are trying to create an environment where all lines run smoothly and continuously. We don't know what we don't know but they are trying to run a smooth business, not placate some customers trying to game their system.
4) I, and others today, were told unequivocally any change, independent of "secret back doors" or where their order stood, would be met with financial and calendar 'penalties' or simply not allowed at all. In other words all orders have been cast in stone, save canceling.
The answer to your question is any or all of the above. Personally, I think it is ALL.
