Yet none of the other mainstream automakers has done so.

Are they even trying? It seems like the only reason to do this is for publicity. Maybe a manufacturer that's known for their ICE vehicles would want an opportunity to show off their electric vehicle engineering but I don't know any it would make a difference for. US manufacturers even sell electric trucks. It's not like any mainstream manufacturer needs to rebrand to sell electric vehicles.

> Are they even trying?

Nope, probably too busy faking emission results, lobbying at the EU parliament , or designing overpriced mid tier cars in the US

Research also might trickle down to production cars. Maybe research for some extreme project has more opportunity to find unexpected improvements compared to more tightly budgeted production research