While Royal will certainly welcome existing cruisers on the short cruisers their main intention with Wonder and Utopia is to go after the new to cruise business which is a huge market.
For existing cruisers it may not appeal but it has a lot of appeal to those who have never cruised. It is not as big of an investment in both time and money to try a new type of vacation that they may be hesitant about trying.
It's all about offering up a brand new product that will draw in new guests to try cruising and then hopefully get them back on board for the longer cruises.
Short vacations, whether it's a weekend to Vegas, Disney, a beach or another city is a huge market that Royal is now going after with some of the best ships they have.