My first cruise was onboard the Carnival Mardi Gras, their very first ship formally known as the Empress of Canada, and she weighed in at an impressive 27,250 GRT. Pretty small by today's standards but hey, my first cruise was in 1982 and Carnival was 10 years old at the time with only 4 cruise ships with the largest at 30,000 GRT. That was the Tropicale and she is still sailing today with Costa cruise lines as the Costa Tropicale.
Now 30,000 GRT won't hardly get you a good lifeboat on one of these behemoths.
My last cruise was on the Carnival Legend weighing in at 88,500 GRT and carrying 2,124 passengers. Now in my opinion this is a perfect sized ship, not too big, not too small.
Why no more small newbuilds, I think it's a little of money and a little of demand. The demand is there for the big stuff and, everybody wants to sail on the biggest! Money, heck the cruise lines make more sailing a big ship with lots more paying passengers.
My 2 cents worth,
Bill 8) 8) 8) 8) 8) 8) 8) 8)