Why are 18th Century Writers Less Popular than 19th and 20th ones, at least the Novelists?

So hello. I posted a thread here a little while ago asking after the academic reception of DH Lawrence and now I have a similar question. As a layman, it's hard to grasp what the "trends' are beyond my own small experience. I'd love to know what people with higher education or who work in higher education can tell me on this.

I've always loved the Romantics - the big six. (which I'm learning were only relatively recently canonized) But I started to wonder "where did they come from?" Blake and the rest of them did not poof into being from nothing. I like philosophy too so of course I knew Rousseau and his influence on the Romantics. But as I am just perusing through books, articles, Wikipedia, I start reading about the Sentimental Novel. I start learning names like Samuel Richardson, who Rousseau loved.

But it's a name I've never heard before. I'm not claiming to be super informed but even the average person might recognize names like Charles Dickens, George Eliot, Jane Austen.... Hell, they'd recognize William Blake who was right there at the tail end of the 18th Century. But Richardson, Henry Fielding, these are apparently two towering figures in 18th Century literature that I don't recognize one bit.

Are they as semi-obscure as I think? If so, is this mainly a popularity thing? Are they studied in academia?

My impression is, if they are studied in academic circles today, not nearly as much as the 19th and 20th Century literary figures. You could drown in monographs and companions to the figures I named, and then you get into early 20th Century British writers who are also very famous, and 19th Century Russian novelists like Tolstoy and Dostoyevsky that basically everybody knows. I can barely find much of anything specifically dedicated to Richardson (who has piqued my interest) and what I have found is decades old.

So yeah, appreciate any insight more learned folks here can give me while I start my reading of Pamela.