drowned has no trident dont discard trident

at first we get a diamond_sword enchanted looting lvl10000 by command.Now we kill a drowned has no trident，he will give us his meat but no trident. we try Many times but the same result.it means that the chance drowned discards trident is 0%.something interesting is that we kill a drowned has trident,he will discard noly one trident.