Porsche had the first hybrid in 1899, BMW built an electric car 40 plus years ago, and Nissan has had electrics longer than Tesla. It would seem obvious that Tesla has no patents that would preclude someone building a competing car. .... and Nissan, Toyota, BMW, Nissan, Porsche, GM and Ford are all going to keep Tesla in the niche category, So, why would any company consider buying an overvalued Tesla?
What you still fail to grasp is that these big players don't want to play in this space. It simply is unconducive to their business models where profits are measured by replacement parts and repeat sales due to fast depreciation. You said it your self. This technology has been around for quite some time....So why have they done nothing with it???