It's not just you guys, we are having the same problem and our group is small. Maybe one or two of us are on at the same time and that's it. I've tried in a single player world also and no luck there either.
Hokay, Two Big issues, here. The first is that Servers, Split the (Hostile) Mobs' Spawning (at last I Wiki-searched for this), Between - often Far-flung from one-another - Players.
So each gets Part of the overall Hostiles' "Spawnage." I don't face this myself, on SP.
The Second issue, is it's an Update. So it May have things being-still learned /looked-at.
I don't get - apparently - as many Drowned - or at least, not with Nautilus Shells /Tridents, that drop - as others do. I've tried looking lots of places, and stayed in the same ones which seem to have more, too.
But one of the conclusions I've drawn - of the Drowned - is that others are simply Playing-more. More than my own, almost-exclusively New Oceans, since 1.13 (and 1.13.1).
More Total-Time, at it. For me, since the Drowned are either there - with stuff in-hand, so I go-for them - or not, so lately I don't; there seem to me though to be as-many: from 1.13 to 1.13.1, but I haven't checked that (focused on the Drowend), either.