What is there to investigate?
They're cheap, they get the job done, and the Chinese will absolutely sell them at a huge loss until they dominate the market.
Why is this happening? Because the West hasn't made an actual cost effective electric vehicle, while the Chinese focused on that almost exclusively over the dumb nonsense of building massive SUVs or luxury sedans as a premium item.
So, investigate the Chinese or whatever, but why don't we try to build a consumer electric vehicle that's actually affordable instead of bitching that China did it first and are using their advantage to demolish the competition.