The large ships may make lots of money but if their destinations continue to be limited their revenue will dry up.
The constant drive to go 'bigger' is sure to have a negative impact at some point...
There are many places now restricting cruise ships due to overtourism. These floating megaships have too many passengers which would cause overcrowding.
Barcelona, Venice, and Marseille are among the cities that have already taken measures.
Santorini has also tightened restrictions on cruise companies. We've been there when there have been four voyager-size ships in port and the streets were crazy busy.
Protests in Norway may have an impact there too.