Have you not read them? You could probably count the fantasy books I've read on one hand but LotR is something unique. The Hobbit is OK but its very different from it's sibling, one is a children's book and the other is a complete mythology. You're right, they were written many years ago but are still held as the benchmark for fantasy literature. Like any massive hit it comes down to appealing to people who wouldn't normally read that genre, the fantasy book to read for none fantasy fans as it were.