Ulmo loves elves. He's always had a special affection for them, even more so than his peers. Maybe because he is the closest to them in a way. Water is almost everywhere, lakes, streams, rivers...and the sea is so great, and the coasts are so long...
Maybe this is why he very gently takes the broken form of the last Fëanorion out of the water where he had thrown himself, and deposits him softly on the coarse sand of the beach.
He watches him shiver, fëa in disarray, wracked with despair, tears streaming still from wide eyes where the light of the trees yet remain. Ulmo watches him trying to scramble back into the water, only for the tide to recede before him. He won't let him follow the silmaril he threw in the waters.
Fire is not his domain, he could not save his brother. But maybe he can save him.