In my opinion, there are a few reasons of why Elon Musk releases their patent to the public. Firstly, he wants to control the standards in the industry and speed up the adoption of electric vehicles. This is aligned with their company’s mission to “accelerate the advent of sustainable transport by bringing compelling mass market electric cars to market as soon as possible.” By obtaining the patents in the first place, he is discouraging any other company from adopting the same technology to innovate and create a mass market for electric vehicles.
Secondly, having competitors who leverage Tesla patent work actually serve as validation such that their technologies are viable and desirable. It can serve as a strategy to allow Tesla to reach a larger crowd – Crossing the Chasm, over a doubting public.
Thirdly, Tesla have made early investments into production facilities like the Gigafactory, they may be able to change their business model such as to manufacture parts for other automobile manufacturers who are in the same playing fields. This will provide them with an alternate revenue stream until the time when those manufacturers have developed their own supply chains.
Lastly, having such an open environment that encourages information sharing may be the best way to spur creativity and allowing Tesla to challenge themselves constantly to innovate and improve in order to stay in the age of technological advancement.