I think it is because most cruisers are American and the temperature that they seem to expect in other places and sometimes their own homes is lower than we would expect but the ships oblige. Remember that each cabin has a thermostat and it works well. We use ours so that the cabin is at the temperature that we like. The cabin stewards will adjust it sometimes and if they do just tell them not to touch. ..... Neil.
When she that must be obeyed asked on our last princess cruise about the temperature,the answer was it helps against seasickness to remain cool....... cheers .
It's easier for people to put additional clothing on than walk around the ship naked I guess...although on a serious note they have to circulate air on the ship I guess as a fairly sealed unit it would get hot fast in there otherwise.
When we were on Serenade of the Seas, Brian their assistant Cruise Director told us that the reason cruise ships maintain a chilly temperature is to help keep any possible instances of the dreaded NoroVirus suppressed. Makes sense. I'd rather have chilly temperatures than an outbreak!