Some of the reasoning I'm seeing for staying in St Petersburg is a larger tract of property, allowing the team/builders/community etc to build more than just a ballpark
https://cms5.revize.com/revize/stpete/Residents/Current Projects/Gas Plant/Hines Rays HGPD Presentation.pdf
These groups are looking for entertainment centers, housing, shopping, restaurants, hotels, etc.
I guess that wasn't available in Yorba City where I understand the alternative was to be located.
I don't know the area, but that's what I've read. My one trip there many years ago found the bridge between Tampa and St Pete a bit daunting.