I'm convinced now this is the reason for NAPA's decision. From the article TRL posted...
"In the days following the race, NAPA’s Facebook page was inundated with angry messages from NASCAR fans; many of whom were also NAPA customers. One after another, thousands of fans vowed to boycott the auto parts distributor, despite the fact that NAPA had no stake in – and no prior knowledge of – MWR’s actions.
NAPA’s sponsorship of MWR was undertaken in an effort to build brand loyalty and increase sales. Now, their involvement has produced the exact opposite effect, costing them business and alienating longtime customers. Scorn, ridicule and lost revenue were not supposed to be part of the deal."