Volvo and Daimler cannot afford for someone else to get there and hold all the patents. If it doesn't work out at all they will lobby and get the laws changed. If it works out though they won't have a strong a position to lobby from (someone else proved it works, why can't you?) and risk losing that side of the business.

That is enough reason for them to put money into R&D. It might or might not result in anything for many different reasons.