It wasn't until last year that Tesla Model 3 surpassed the Nissan Leaf to be the best selling electric car. I know the Leaf is not as competitive in some ways, but it's sold in the US for years with plenty of success.
Leaf is a cheap way to go green. Low performance, outdated UI, but pretty cheap.
Tesla is going green in style. Minimalism, performance, at a slight premium to ICE.
One thing to note is that leaf is one of the WORST vehicles values at % of resale value retained after 3-5 years, while Tesla is one of the best. So the market is very clearly looking for used Tesla over used Leaf.