"Where's our traffic?" is heard by ATC as "why aren't we number 1?" and thus assigned the label whinge.
You already know why you're being vectored because you'll have heard it on first contact with approach. "Vectoring for the ILS" or whatever the approach happens to be, or it'll be in the STAR to "expect vectors". A vector is not just a heading; think back to those vector diagrams you drew in nav training and at school. A vector is a heading at a specified speed. We are not required to tell you where traffic is from which you're separated (except in Canada where we do have to give traffic if your blips will merge at minimum vertical sep).
If you're hoping from a visual approach and you're number 2, by all means ask for the traffic so you can follow it. If you just want to whinge about slowing down or being widened out, try to act your age.
