Curious since every year or so I start wondering how to make a better ski daytrip carpooling network. Despite having various ideas / mockups, the best solution still seems (which is what I use in WA) to just use a meetup.com group with decent communication and pre-defined prices for a few well-known end-destinations.
I don't have any data to back it up, but I suspect that BlaBlaCar has been under pressure in Germany in the past few years. For a long time competition in intercity buses was restricted, and while cheaper than taking the train, was still quite expensive. BlaBlaCar was cheaper, and expanded into a lot of non-consumption of intercity travel at the time. Once low-cost bus service came in from companies like FlixBus it was often cheaper to take the bus than to rideshare, with more predictability and less co-ordination problems. Deutche Bahn as also provided more low-cost runs in response to this competition, though they seem to purposely make it hard to find these trains on the bahn.de website, while they are easy to get through aggregators that show cheaper modes of travel.
That said, there are a lot of operators on BlaBlaCar that operate counter to the law. Many people I know who use the service regularly have a story of going to meet with a driver who looked like a 25 year old blond German woman in the profile picture and discovering they were riding in an 8-seat van driven by a 40 year old immigrant.
 You can get an idea of different costs at the aggregator busradar, though they don't list every provider. https://www.busradar.com/search/?From=Berlin&To=Düsseldorf&W...
As a driver, I'd be totally up for splitting the gas money with someone, but as a passenger it just seems like a more expensive offering with no increase in benefits for me.
Are European buses or trains more expensive?
Drivers have to coordinate pick up and drop off of passengers, which is a pain, especially in LA. On the other hand, passengers getting dropped off can also be a huge benefit since the bus stop probably isn't your final destination.
In general, Europe is denser (more cities within a closer distance), gas prices are higher, and people are maybe more trusting of strangers.
I admit that it's also a great way to travel to an airport in a nearby city (which is how I use it), but I probably wouldn't use it if it was more expensive.