It’s more likely that tickets are more expensive now, plus the effect of date-based tickets. Your ticket is worth the online price for a 5 day PH in 2017 (not the current price) and now you have to pay the difference between that and the current price of a 6 day PH for the specific dates you want to go.
Yes, you are right, it is more expensive now. I checked and the same ticket, like they said, is over $200 more. I am shocked that in 4 years it went up by that much. It's not even an adult ticket. It's a child's ticket for my granddaughter.