Because they're about 2 times the price.
Figuarts Luke: 4870 Japanese Yen on Amiami before shipping.
Black Series Luke: US$19.99 in stores.
Current conversion rate puts Amiami at about US$39.55. Amiami also puts a fairly hefty discount on their products, it's about $48.23 if you didn't have a discount at all.
In addition, due their extensive dealings with adult fans, Bandai has more experience in catering to their wishes. The proximity to China also means a much faster turnaround on any production samples, whereas it takes quite a bit longer for Hasbro to get in any test shots that are sent their way.
Does it excuse everything? No, but they need to be considered before saying 'better' without any context, it's best to realize it's a case of 'you get what you pay for'.
