My total anecdotal opinion is that there are fewer standard surveys (should the guy flip the switch on the train tracks to kill 1 guy versus 5 guys?) since in the summer, there are fewer students in Psych 101 who have to post surveys for class. But there are surveys for PhD students who take the summer to work on their projects hardcore or other researchers who use the summer to work on personal projects that need to use MTurk. And non-university product research kind of stuff always runs all year long.