Would they? You could say the same if the entrants were energy drinks, horse sperm traders, privateer drivers or WRC2027 constructors. Not sure what ROI measurement you'd use, but car companies...
Maybe it's because the sport is rebuilding itself again and it will take some time before sponsors come. WRX died and ERX take all burden on it's shoulders to carry on. I think it will get better, at...
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I think they made it even worse with completely locked out content thinking that hardcore fans will paying for that, but they achieved quite opposite effect. Many of them become casual fans. Well...

I in general wonder what manufacturers get out of motorsport in detail, but since some series are very active in this regard, there must be a ROI somewhere to be had. Hopefully we have some people...
WRC mainclass from 2027