its less about the subsidies and more that budget buyers in the U.S in particular are very picky buyers.
while the federal/state EV tax credits, you can get vehicles like the Chevy Bolt for 20-22k. regardless the car still isnt that popular (meaning theres something specific about the car that buyers dont want).
for those buying used cars, theres not mamy reasons why someone would buy a say new 18k-20k EV that had many cuts in design vs an older premium EV. Used 2016 Model S for example can be found near 16k. its a new cheap car vs used premium car debate
this places a burden any any auto maker trying to make a budget car, because in order for it to sell well, they need to have razor thin margins, and sell a lot. failure to do so would spell the end of your compamy due to how many you produced.