Welp, it's now towards the end of August, and DEF CON and CCCamp are over, so it's probably time to restart this discussion.
I purchased my ticket through the mobile Universe site and didn't even see this option because it was further down the page.
TBH, bundling parking with a certain kind of ticket is a very weird way to do it. You basically have to forfeit the early bird discounts to get parking?? Between that, paid parking being new, and it not being easily seen on mobile is probably why it's not taking off. I'm also not going to buy a second ticket just in case I end up needing a parking pass -- that just creates more chaos.
In my experience, it's also way too far in advance to be making plans on how to get to camp and back. Traditionally that has usually happened when ferry reservations are about to open, but I've also been in situations where we've been trying to figure out carpools up until a few days before camp. It usually ends up being a bin-packing/constraint satisfaction problem that is not trivial to solve.
I assume paid parking was introduced to encourage people to carpool, but with extremely limited ferry spots, that was already happening. I'm not sure additional incentives are needed.
I don't know what your options are with Universe now, but I'd really consider selling parking passes separately, stop selling the combined ticket/parking pass, and offering refund options to people.