Breeders were based on unrealistic projections of there being a thousand reactors in the US by the year 2000. Under such extreme growth, uranium would be getting scarce, so breeding would be needed.

But that didn't happen, and, absent uranium shortages, breeder reactors are more expensive than ordinary thermal reactors. There's also the small problem of fast breeders being potentially subject to prompt fast supercriticality during a meltdown. That's one of the few ways to make an accident worse than Chernobyl.