In terms of increase cruising demand, Royal is appealing to a broader audience than it did 10-15 years. Building on that specifically in the last few years. No one was deciding between Disney vacation and going on Sovereign of the Seas. As much derided on these forums, its the families with kids that 20 years ago were unlikely to consider a cruise the ones booking now.
As for affordability, Florida has 23 million people. 23 million that can drive to a port vs. dropping $1k+ on flights/rental car etc. on other vacation options. A week anywhere in the US that requires a flight, hotel, rental car can be the equivalent of an Icon cruise for a family in Florida.