I think it more comes down to focus. Right now Orlando is focused on grieving this tragedy. Many of the theme park employees were personally effected by this either knowing someone who knows a victim or personally knowing a victim. So Universal and Disney decided to not take the focus away from the grieving process and putting it on them and their new attractions.
I also think that both are businesses and in some ways used this to delay the media events. Neither Frozen or Kong are ready for a grand opening. So this gives both parks more time. So delaying this was a win for the community, the employees, and the parks.