Some common sense is helpful here. If the frequency is going b@lls out, the reason you haven't been told why you're being put on the heading or given a change of level (i.e. a revision to a climb or descent clearance that stops off early) is because the controller probably has little enough time to think never mind tell everyone what the plan is. If it's quieter the controller will probably give you the information - if it's that quiet yopu'll probably go in a straight line wherever you're trying to get to anyway.
In the old days, before TCAS, I can understand that a pilot might have wanted more info but these days the close in situational awareness to avoid a collision is largely provided by TCAS - so I can only conclude that the requests made by pilots for traffic info are made for less significant reasons.
I've been in the ATC business for a good many years and if there's one thing I can promise you it's that controllers do not put aircraft on a heading or stop it off unless there's a good reason. And that reason will almost inevitably be another aircraft or some similar good reason. I can't speak for others but I won't do it because it increases my workload and I'm lazy. The upshot is that even if you ask where the traffic is, and I tell you, it's not going to change anything.
One final thought. If a pilot refuses a clearance that I issue but doesn't say why I'm not going to ask why - I'll assume there's a good reason and sort something else out.