Looking at the event page, it looks as though the summer sensation is more of a marketing, than an actual event. The whitsun half term had no event, so maybe looking at lower key events without big act at times when people are likely to visit and targeting events when they may struggle. I haven't been since January for various reasons, so hard for me to comment, but if they are busy through ticketing events that are attracting more people and revenue, then maybe they are looking at fewer events that are labour intensive and utilising summer with theme that might not be classified as a full event, but utilises sand beach and summer food etc without big acts with costs being higher.
Hopefully they are able to have full ride offering and creating summer offering.