> why should there be tax incentives at all for a product that is wildly popular and seeing adoption even without a tax credit?

To reduce air pollution and combat climate change. To encourage ICE manufacturers to switch.

The point is that the tipping point has already been reached. People who want electric vehicles are going to buy one, with or without the tax credit. Those who don't (e.g. because they can't have a charger where they live) aren't going to be swayed by the tax credit. It's not clear it has any effect on EV adoption anymore.