I wonder to what degree company size and current employee wage plays a role in this (in the U.S. the pressure to not share salary with coworkers tried a wrench

I wonder to what degree company size and current employee wage plays a role in this (in the U.S. the pressure to not share salary with coworkers tried a wrench in this theory). Given a shortage, raising starting wages would encourage people to change jobs, however employees (recently hired or existing) before the increase would also want that new increased rate. Combined with companies hiring thousands (think Walmart) a wage increase becomes multiple millions per year (that's a lot harder to sell to a board)