Why would they do such a thing?

Norwegian Cruise Line is banning Chinese passport holders from their ships:

Ming Yang, a permanent resident of Canada for 15 years, was supposed to sail from Florida on a seven-day cruise with nine family members and friends this weekend, but a new Norwegian Cruise Line policy states the company will deny boarding to anyone holding a Chinese, Hong Kong or Macau passport, regardless of where they live. [...]

"I feel I've been targeted just because I am a Chinese passport holder," Yang said. "The policy is very racist, and it's targeting a certain race."

Ding ding ding! You win the grand prize: fresh bat soup with monkey brain chunks!

The cruise line also states it will deny boarding to anyone who has visited, or was in transit through, China, Hong Kong and Macau within the past 30 days.

Quite reasonable, indeed.