Sam2. I think it is because the Yeshivish world is terrified of calls for change even if warrented. Especially when it is called for by “animal rights activists” or scientists or those perceived as “liberal”
Lior Kapparos as practiced today has zero to do with the Rema. In the Rema’s days people had chickens so once a year before shecting it anyway they twirled it around their head first. I assure you the Rema didnt have thousands of chickens trucked into to cite is from who knows where then stored in the sun with little food and water. Then to be shechted and discarded. And no most of the cickens do not go to the poor. There is too much effort to clean all thos echickens most are killed and thrown in the garbage. This was not the minhag as practiced byt the Rema or even a mere century ago.