Moreover, they would be considerably more expensive than existing plants (especially if fuel is to be reprocessed), so they're nonstarters.
The big problem with fission is that it's too expensive. Fast reactors make that main problem worse. There is no economic margin to do fancy (and expensive) things to try to address the lesser issue of nuclear waste.
In an economic sense, when compared to burner reactors, this is correct. As the rise of wind and solar has shown however, political will and popularity matter more than pure economics. Burner reactors are more of a 22nd century technology, assuming the grid storage problem doesn’t get solved by then and we just go full renewable on economics. But nothing is set in stone