Because, it does not destroy all waste, despite a cartoon claiming as such and gullible people falling for it? Even "short-term" waste needs to be stored somewhere for about 500 years. Sure, it ain't like the others in terms of length of time but anyone who thinks that is a cheap fact or trivial is an idealogue. Since they can exist at both extremes.

So the issue of the water table or general environmental contamination is not addressed the way OP claims. There are also higher costs and higher grade fuel is required. Not to say that there are not some advantages but the cartoon is just plain incorrect and taking a toodler's view on some serious concerns. The Wikipedia article has a list of disavantages for anyone to look into.

https://en.m.wikipedia.org/wiki/Fast-neutron_reactor