The majority of LA born NFL fans are Raider fans. The Rams played in Anaheim, which is basically a different country, before they left a generation a ago. Now they're back playing in what was the Raiders home stadium. What's left of that Rams fanbase from 20 years ago (not much) is unlikely to trek it to South Central and the Coliseum.
It's going to take time to build that following but I'm confident once the new stadium is there, they'll be fine. You just can't expect LA to fill, or even halfway fill, a 90K seat stadium for a "home" team not many people out here care about (yet).
As far as the Chargers go, they're playing in Carson, which is also in a different universe than LA proper. Nobody here is a Charger fan. They're playing in a soccer stadium. Nobody really wants them here.
That being said, once they get into the new stadium people will come. As far as the $100 parking goes, that was for a tailgate lot. For USC games at the Coliseum, to get those premiere tailgate lot parking passes next to the stadium it takes a ridiculous donation, in the thousands of dollars. I'm sure you can find parking somewhere near the stadium in Carson for far less than 100 bucks. The spotlight on the $100 for parking story seems to be part of this calculated negative campaign being conducted by an SD based anti-Spanos/NFL faction. They put up
these three billboards right near the stadium.
It's really not far to compare the NFL attendance to that of USC's attendance. They've been in the Coliseum forever and the school is right across the street. The fans know what the deal is and the tailgate for those games is a blast. It's an up year so home attendance is going to be high.
Bottom line, it's unfair to judge the NFL's move to LA after only a few weeks. You have two teams with non-existent fanbases playing in stadiums they don't belong in. The sportsbars in LA are packed on NFL Sundays and most of the people out here are transplants rooting for the teams they grew up following. It's a city full of frontrunners though so if and when the Rams/Chargers turn it around the stadium will be rocking with we're #1 $75 foam fingers. Angelinos like new, trendy, upscale things so I guarantee the new stadium will sell out when it opens in 2020 or whenever it does.