The economy of SXM is essentially based on tourism and cruises are a highly seasonal activity. From the same token there are no Alaska cruises in winter, there are much fewer Caribbean cruises in summer. In order for these humongous cruise ships to dock in SXM in peak season, SXM had to expand its cruise terminal the same way airports have to be adapted for the Airbus 380 and its 500+ passengers. So, if SXM undertakes the transformations to accomodate these ships, they would have no reason to limit the number of arrivals. They did the same with the airport a few years ago and they built the causeway to cope with the increase in road traffic so it shouldn't be a surprise to anyone that tourism in SXM will continue to grow, with both the good and the bad consequences associated with it.
If SXM doesn't adapt to the increase in demand, guess what, cruise lines will stop somewhere else. It's not that there are no other islands in the Caribbean where they could stop, starting with Cuba a few years from now.
My 2cts.