Delta has a flexible date award search feature. Using the the 5 week search, I see plenty of dates in August at 19K RT. If you have a bit of flexibility in departure or return dates, I think you should be able to find a 19K redemption. I doubt this has anything to do with cookies (and this can be easily checked by clearing cookies or using a different browser). As others have noted, unlike JetBlue or Southwest, there is no attempt by United, Delta, or American to tie or correlate revenue ticket pricing to award point redemptions. So don't get hung up on with the relationship with award pricing and revenue prices.
Thank you. I'm specifically going weekend of my bday, so the only flexibility I may have is coming back a day later (which I see is 5k less points), but I'll need to weigh that cost versus the extra hotel night.
I don't fly much, and when I do it's usually SW, so I had no idea other carriers didn't have set price to points/miles structures. Seeing different miles requirements for flights with the same price really threw me off lol.