There are several inaccuracies and inconsistencies in this.

- Elrond knew of Tom Bombadil.

- Tom Bombadil had heard about Frodo's journey from both elves and hobbits. I.e. He was known to and communicated with both.

- Was there not a hobbit song about him?

As to why the hobbits had little to do with Tom Bombadil...

- A character of his power could easily have chosen to wipe the hobbits memories. Maybe this was his usual approach to hobbit intruders?

- Another possibility it that given Hobbits extreme social taboo about adventures and their fetish for respectability it is quite possible that many hobbits had interacted with Tom Bombadil but few talked about it (e.g. Farmer Maggot).