and nobody seems to be going june-august
Welcome to cruise-chat.
Actually many people go during those months. The Liberty Of The Seas will probably be sailing at or near maximum capacity most weeks. This is when we have to cruise since we have a school-aged son, and thus the ships have lots of kids aboard in the summer. Pricing during June, July, and most of August is much higher than during most other parts of the year.
Weather varies. The Eastern ports have surprisingly moderate summers. I think it is warmer and more humid in Alabama in July than it is in St. Thomas.