Lamplight and PaintIt have is right; chrome plating a bike is very labor intensive (polishing the bare steel to a mirror finish), then nickel plating, and finally chrome plating. After all of that, the frame has to be baked for several hours to relieve hydrogen embrittlement. Also, there are evironmental laws that have caused many platers to just fold up shop. In any case, to do a decent job is very expensive.
CyclArt has a very good write-up on the process
HERE, and it includes what's required just to plate the lugs (basically, much of the frame around the lugs has to be plated as well, then the lugs are masked as the frame is painted).