They are trying to get past the SeaWorld name and brand. It is a damaged brand, and the end of keeping marine mammals in captivity is in sight at this point. It's only a matter of time before the parks themselves are rebranded as well.
They may have found the SeaWorld name on the Sesame Parks was deterring some guests (young parents) from visiting, and they are looking to expand with that branding.
I agree, it's a lackluster name, but it sheds some of the baggage of the past. I follow news from many theme parks, and I have google alerts set for many park names. The "SeaWorld" alert goes off constantly with PETA press releases about how horrible the parks are, news of a helicopter crash that killed several people on Christmas at the SeaWorld park in Australia, and articles about every other marine life park with negative publicity mentioning SeaWorld and Blackfish as part of the story. They have a new vision for the SeaWorld Parks focusing less and less on the marine life, and as they shed the branding over time they needed to start with the company name.