Anything mass produced is inferior to custom fattened and locally raised Beef. Costco is no different. They buy from brokers and the beef is fattened in large feed lots, with thousands of head wallowing in feces and they are injected with growth hormones, steroids and what ever they can get away with, to artificially increase the animals weight.
They are also fed concentrated pellet forms of feed and their bodies cannot process it effectively. No wonder that commercially mass produced Beef is so bland and tough. I have had Costco Beef and it is no different from all the other crap that comes from those feed lots.