Because many, if not most of the demontard party elites convinced their sheeple that so called climate change was an existential threat to humanity. So, in spite of the "fit and finish" problems Tesla is infamous for, their cars run pretty well, at least for EVs. And for a while there, short of brands like Fisker, Tesla was the main player in the EV game. So if the run of the mill, 'I-just-got-to-feel-good-about-myself' democrat wanted to make the cool SJW statement with their car purchase, Tesla was the only way to go.
Besides, just like children are with shiny new toys, Libs seemed to be transfixed by how quickly they accelerate, just like a golf cart.