So, why were Ford, GM and Stellantis there but Tesla wasn't? Because Tesla was already making EVs only, because none of its workforce is a part of UAW (due to Tesla being anti-union) and because this EO had no impact on Tesla's workforce what so ever. Elon being butthurt about it doesn't change the fact that it would've made zero sense to have Tesla there.
You don't have to take my word for it, Jen Psaki directly addressed this at a press briefing:
> Asked if Tesla being a nonunion company was the reason it wasn’t included Thursday, Psaki replied, “Well, these are the three largest employers of the United Auto Workers, so I’ll let you draw your own conclusions.”
https://edition.cnn.com/2021/08/05/business/tesla-snub-white...