It was once, then newer generations started replacing the older ones. Why should they know?
Here's the thing, before the early noughties or so there was more shared culture between generations. Blame the Internet or Gen X taking seriously the culture of their elders as something they had to check out because culture is culture man. Imagine finding out that the young ones just care about their own generation memes and media. I don't know what Gen Z is going talk about with Gen ZZ , probably just basic facts about food and the like, it's all tiny bubbles nowadays.
The point is pre-teen me had already seen about a dozen Belmondo films in Spanish RTVE by the time I discovered I really had to see À bout de souffle because of FOMO. He was the picture of charismatic French actor for a long time. Actors were more important back then and people knew about more actors, and about more older movies too I guess.