Sooo many things can change EDDs dynamically. Just a few of the things I can think of right off hand are:
- Weather
- Material shortages
- Transportation problems (rail or hauler doesn't show up on time causing a shift in logistics)
- Order changes and cancellations (example: one or more orders scheduled for a rail car or hauler get canceled altering the logistics)
- Not as many orders as expected for a given delivery location
- Production problems (unexpected equipment failure or process correction required)
- Other things I forgot or am not aware of
It's truly mind-blowing to me how two factories can manufacture and distribute nearly a thousand Model Ys per day and deliver them nationwide as efficiently and accurately as they do. There's a lot of collective knowledge at work here.
It's easy for one person to get upset because their order doesn't arrive when expected, but so many things have to come together at exactly the right time to produce the desired result. It's not like Tesla has a giant warehouse filled with 100,000 Model Ys that they can pick and ship for next-day delivery.
They're having to source materials in near real time to meet the demands of thousands of impatient buyers per day and rely on other companies to do their jobs exactly when expected to make these deliveries happen. A lot can go wrong and it often does.
Each of us thinks our individual orders are more important than they really are. The collective of orders is important, but each of our individual orders isn't even a blip on the radar.