It is not difficult to guess the reasons for this step. With internal cells, Tesla has been able to optimize its battery packs for cars, whether it's a longer range, faster acceleration or more sustainable performance. This could also lead to cost reductions by eliminating intermediaries such as Panasonic, making $ 25,000 more viable.
In addition, this could provide resilience if the relationship between Tesla and Panasonic goes south. The Japanese company has recently frozen its investment in Tesla's Gigafactories and recently reached an agreement with Toyota to manufacture car batteries. Elon Musk also blamed Panasonic for acting as a "caveat" for the Model 3 production. Internally developed cells could ensure that Tesla is not held back and, as Technology Vice President Drew Baglino put it, make the company a "master of our own destiny."
This does not mean that Tesla Panasonic will drop completely. It needs its partner in the short term, and Panasonic's capacity could be crucial as Tesla expands its reach. Panasonic may only want a backup plan if it is no longer the center of Tesla's universe.