I hadn't really thought about it all that much. Not sure just how many #1s you have checked, but I checked a few with a magnet and as far as I can tell ALL factory #1 triggers are non ferrus going all the way back to non prefix models made in 1968.
The only ones I have that have steel triggers, have after market triggers, Canjar and Kepplinger.
Now I don't know why that is and I didn't test them all but my earliest, dog leg bolt 77s , seem to have a steel trigger. At least it attracts the same magnet that none of my factory #1s do,
I guess we could get a big push going to add a steel trigger. Of course it also well might add add to the MSRP somewhere between $125 and $225 if we use the now defunct Canjar or the very classy Kipplinger as a model for what it might add???
RWT