Seriously, why didn't they retooled all factories for the highland launch at the same time? Did they had too much inventory of part for the older Model 3 in the USA? The Y Chinese update is also really mild but the Model 3 makes sense. I am surprised that the stock is not down more than the 2.5% so far.
Seriously, the primary reason is that each factory thus far has been a large advance on each prior one, with the famously 'kludgey' but impossibly cheap, Fremont the hardest to scale and each successive plant reflecting the 'state of the art' when it was built. That really si the primary reason why each factory is no now a mirror image of each other, so they each must be updates in sequence. Similarly, they shut down one factory at a time so they do not lose as much production as they would if done at the same time. As an added factor, each factory has local suppliers and some battery flavors (e.g. BYD) serve only one factory, and each factory has local variations as well, so no two factories are exactly identical. Perhaps the easiest illustration is to note which factories have enough Gigapress capacity to have both front and rear castings for Model Y and which do not. That alone makes factory updates quiet different from one factory to another.
I am certainly not a manufacturing specialist. I do understand the impact of the Brandenburg paint shop vs those of Shanghai, Austin and Fremont. Add those to all the other differences and we can see that the very flexibility of TSLA production evolution carries with it massive version control implications from product to product, factory to factory and supplier to supplier. Logistics alone would overwhelm an effort to make every factory identical.
This question rarely arises for other OEM cases because almost nobody other than internal engineers pays attention to factory homogeneity.
Just as an illustration, think about Tesla Model Y having just become the largest global car sales champion replacing Toyota Corolla.. The Model Y has the same form factor globally, even though manufacturing differs between each factory. The Corolla, by contrast, has a plethora of models with unique body styles, drive trains and branding variants, all of which aggregate as "Toyota Corolla" for sales reporting, but nothing much else:
en.wikipedia.org
When we assume that Tesla, approaching two million sales per annum, should have all factories upgrade simultaneously, we are forgetting how different the products and production processes are in each factory. Tesla makes it look easy. That is part of the incredible complexity that Tesla manages almost invisibly.
We heard all about that when Tesla adapted to whatever semiconductor they could get during the supply criss while others had to stop production. Spectacular and wonderful!! Now, just think about version control and individual factory differences. It is amazing that they're able to make all that seem easy. They cannot quite do the same upgrade to each line for each model at the same time.