Because they barely passed their 8th-grade Science class.
Dunning-Kruger Effect in full bloom!
Natural Uranium has a U-238 content of 99.3%, while the other 0.7% is the U-235 you need to make fission bombs.
DEPLETED Uranium consists almost entirely of U-238, which has a half-life of 4.5 billion years, meaning that it is relatively harmless to handle.
Regards,
If memory serves from the Iraq wars and I believe it does, there are two kinds of DU; one is harmless, the other isn’t.