I think his point is mostly that what I guess one could call the old world intellectual culture is gone. The one defined by having read and studied the classics at a century old university.

We have abandoned the former minority culture, which was truth-seeking, profound, quiet and subtle, in favour of mainstream or mass entertainment,

This intellectual culture could only exist because people had a shared set of experiences, i.e. they had read the same texts, studied the same topics, heard the same pieces of music and so on. While obviously everyone hadn't read exactly the same things, but there was still a large overlap. Basically while everyone hadn't read every greek text on the topic of philosphy most had read Plato and even if they hadn't read all the same texts on mathematics most had read Euclid.

The situation we have now is that there is so much you can study and so many people you can discuss with that it creates these focused speciality cultures because peopel just don't feel that reading some text about a topic they aren't interested in just isn't worth it. Meanwhile in the ye olde world the reality was that people didn't study Euclid because they liked geometry, they studied Euclid because if you didn't know about that stuff you have a huge gap in your mental tool set.

But now there are people that ONLY study mathematics, history, art, etc. and usually focus in on extremely narrow topics within those fields such as number theory, the french revolution or 19th century Russian romantic paintings. This creates the exact opposite of a culture, it produces hundreds of sub-cultures which primary uniting factor is mass-media stuff like whatever is on TV or the radio.