The early LED replacement bulbs were bad and flickery, they are better now. They even make add on boards to smooth the on/off state to mimic incandescent bulbs https://www.cometpinball.com/collections/led-ocd-boards
I wonder if the places I've been to just don't know, or just haven't upgraded yet (waiting until the originals die?), or are trying to save pennies on the dollar on repairs?