As more companies adopt this "we cover it" guarantee, they're going to start having more "costs" dealing with human drivers. Accidents, time/speed inefficiencies (vs. following the letter of the law), etc.
As a result, they'll start pushing the driverless cars harder. For those they can't convince with the carrot of incentives to make the switch, they'll eventually pull out the stick of passing the costs to those human drivers through various lobbying channels - forcing them to deal with higher insurance premiums, more tracking technology, tiered registration costs for cars, etc.
Corporations with any clout always try to cut their costs - one way or another.