I think that's a pretty privileged viewpoint. That's $100/year of disposable income for maybe a parking spot where you want to go, maybe available when you want to go. That's definitely not a trivial dollar amount for something like that, especially when there are free alternatives (strip mall parking lots, rest stops, federal lands, moving between neighborhoods, etc.). Then there's the question of being able to offer a designated parking spot (hosting) in exchange for staying credits. Paid private parking, especially extra spots, is an absurd luxury in much of the country, for many people.
I knew many people -- climbers, travelers, dirtbaggers, backpackers -- who really wanted to see the public lands that they partially own but could not afford to travel in luxury, people who ate ramen and rice and beans for months just to be able to afford to see the lands. There are also people who live in campers and vans because they can't afford rent. That $100 could definitely go to better uses.
If $100 is nothing to you, perhaps you're the kind of traveler this website is targeting. It's definitely not for everyone. I've met many amazing people on Couchsurfing and Warmshowers, which (at the time) were totally free and still today are much cheaper. The vast majority of the people I hosted were very poor but very well traveled, with stories to tell and friendships across the world. Very few of the rich people I've met have had the same experiences to share. Hosting them was a privilege, and not something I would've wanted to charge them for even if I could. I also met very interesting hosts traveling the same way, because at the end day doing that becomes way more relational and way less transactional -- the opposite of luxury travel.