Ink costs money and pay somebody to number each one costs money too + SideShow is cheap so...
Come on. That's a BS excuse if SSC chooses to use it. They already number most of their pieces and have people that do it. It's not like it would cost much and it would be a very cheap compromise for all of their customers that hate open ES.
Just about every collector would like numbers on the pieces that they order. There may be some people that don't care but I think it's safe to say they are in the minority. I have yet to see anyone here say they will not buy a statue if there is a number on the base.