In our society, the entire human knowledge base has become so huge that no human on earth can learn it all anymore. Moreover, as explained by Adam Smith (FR) and later on Milton Friedman (EN), division of labor has encouraged people to get specialized. I believe that it is a poor constraint that we satisfy.
Fortunately, plenty of talented people popularize concepts they are specialized in, but they are very difficult to fing in the youtube Jungle. I speak about them a lot, I really believe every one should follow most of them and I have decided to share here links to their channels, for friends, former students or anybody that would find it useful.