First time I played, I hardly ever queued for BGs and when I did, it was mostly on dead hours. If I was lucky enough, I'd get one pop a day, no matter which bracket it was. Of course, after hitting 70, it was totally different.
For my second character, I tried peak hours and it worked wonderfully! Every single bracket except for 50-59 were active enough for me to play 10+ times a day while I waited between queues, questing. But ever since RDF has been enabled, people at low levels stay queued for RDF rather than BGs. It dropped the number of players in BGs by a ton!
Honestly, I've never seen people ask others to join BGs at 80. There are times when I'm playing in the 20th on-going BG. So, after you hit 70, the two brackets are pretty active! But you'll definitely see people asking others to join WG since most players don't. I talk around with Lvl 80s quite a lot and the one thing I know for sure is that a very high pop of players prefer PvE over PvP.
If you really want PvP promoted, vote for cross-realm BGs and Arenas.