The lack of a major hack of Apple Pay, Samsung Pay, or Google Wallet probably convinced Costco those solutions are secure.
Retailers are afraid of lawsuits from consumers who lost financial numbers to hackers. Target (NYSE: TGT) paid $39 million to settle such a suit in 2015.
Retailers like Costco might abandon NFC payment if crooks crack Apple Pay. Given the volume of Apple Pay transactions; over one billion in 2nd Quarter 2018 Tim Cook bragged, it is only a matter of time before some criminal genius cracks its encryption.