I just got off chat with HGV and they are claiming what some have suspected: that the developer has monopolized all the availability for the rest of the year, loading it into hilton.com for cash reservations. The only chance you'll nab a reservation at Ocean Oak is if you pay cash or the stars align and you can grab an existing reservation made by another member. Ocean Oak might as well not be on HGV's page for the rest of 2020. I'm not happy and I let HGV know it.
Here's HGV's response (through Facebook chat):
audirt, we were able to look into this further. Please know there are several reasons why you may see HGV availability somewhere else (such as hilton.com). HGV Club Members only have access to inventory that has been sold. Any inventory owned by a developer or an affiliated resort that has not been sold may be made available for rental. This revenue contributes to annual maintenance fees for weeks that have not been sold. With this being said, a Member who has confirmed the same dates you are looking to book may cancel their reservation, freeing up space for another Club Member. I urge you to keep checking for your desired dates and let us know if you have additional questions.