You can do a 1-2-1 with more space than UA, LY just chose not to, because, LY.
I imagine it's not easy for LY on a
787 to have the same seat width, let alone more, than LY on a
777... If it were, don't you think they would have done it?
There are only two things airline can change to accomplish that: aisle width and/or non-seat seat width. There must be some rationale (legal, business, or otherwise) that precluded that option.