Might be the production _rate_ for the previous models doesn't mesh well with their suppliers. We buy plastics in runs of 15,000 parts. It takes us a couple of months to go through those. And then we order more. The manufacturer doesn't make 200 parts a day. Or 1000 a week. The do a full run of 5-20,000 every three months. Which takes them a whole day, once the machine is setup they run it till the order is filled. Sometimes it's obvious they do higher runs and then break up the shipments.

Okay so our products are cheap and simple. But our yearly totals of 50,000 to 100,000 units is comparable to the what Tesla is hoping to get out the door. Tesla's numbers for previous models weren't nearly that high. Gonna be hard to just in time that.

Personal feeling. What an automaker is doing by outsourcing parts to suppliers and then making them manage inventory is. a) they as someone mentioned, keep the inventory management away from the production line. And importantly allowing suppliers to apply higher levels of scale then you could other wise. Important because likely many of Tesla's suppliers production machinery has vastly more capacity then Tesla needs. Telsa and other automakers are thus 'renting' time on those machines.

Frankly I think Tesla is ramping to this scale for the first time, it's bound to be a mess.