I have nine Indian runners. The three originals -- two years old -- will always eat out of my hand, probably just to nudge out the others. Two of my newer hens will NEVER eat out of my hand, and the rest can be hand fed, if and when they feel like it.
I have tried every strategy I can imagine, and neither Claire nor Blair (not intentionally rhyming names; latecomer Blair is simply the LOUDEST duck ever) will ever let me even touch them in passing.
I don't understand the minds of ducks, but I still adore them.
Trauma seems to affect birds in unusual ways. After her coop mates were murdered by a mink, my Buff Orp suddenly craved my attention, was fine with being held and still loves grapes out of my hand. But, in the last couple of months, Honey has decided that she prefers to NEVER be picked up. Hey, my birds rule the roost; I just live here.
Good luck with all the good advice from others. I hope you get them eating out of your hand again. I don't know why people use the phrase "pecked to death by ducks." The sensation of their little bills scooping food out of my hand always makes me happy.