Old books are in the public domain, which means publishers and authors don't make money on them, which means they don't get promoted as much, which means fewer people hear about them and read them.
Also, people may want to read about what they are most familiar with, which is recent/current events. Also, very old works are written in a style that takes more work to read or that requires more training to understand. Even English works that are over a century or so old have many unfamiliar words because language changes and things that were once familiar have now become esoteric.
Some people like that challenge of figuring those things out, but many don't and would rather just breeze through some popular novel.