It is easier to chrome the whole frame by dipping it whole into the plating tanks rather than by just one area at a time. The areas that are to be covered by paint are not polished to the same extent, if even at all, as the paint does not stick as well to the very polished/plated areas. The polishing before plating is the most time intensive and expensive part of the process and the BB area with all it's nooks and crannies is very difficult to get polished properly.

vjp