"And when young people riot, it seems they do it not for the real meaning of the cause but for an excuse to skip school and to have some kind of party."

It has always been like that. There were huge demonstrations against the Vietnam War draft, which was a real mortal concern for young men, in the USA in the late 1960s and early 1970s. After conscription ended in 1972 the demonstrations ended and there were huge music festivals, which have continued to our own time. They are a rite of passage for many young people. Of course the people putting on the festivals and the performers make money, which is the reaon why people generally work for things.

There were kids in the street for the BLM protests in 2020, and that has completely disappeared and the festivals continue. A "cause" requires a whole other level of responsibility from a young person, which is why most of them are reluctant to join some organization except in a make believe way online. They aren't going to sign up to go to meetings or pay dues. They don't want another person telling them what to do. it's more fun to go to shows, or bars, or games and get loaded and have sex, just like their forbears. I wonder if Greta Thunberg, who is now 19, has ever drank a beer which she can do legally, although the Swedes are really down on cannabis. The party will continue in any case.