Visited The Cross Roads, not a single player there. I was surprised to see 2 players on Thunderbluff. Been away for over 9 years. It seemed kinda sad. I love this game and I hope to stay awhile.
Lots of the old areas are very quiet. If you want activity, you’ll need to head to the newer expansion areas or cities. I’ve run across quite a lot of folks in Legion content, and when I move on to BfA content, I’m expecting to see more. The lower-level areas, though, are really inactive compared to how they were in the beginnings. I had a love-hate relationship with XR and Tarren Mill way back then; the PvP was fun, but made it hard to focus on leveling!
RP realms are only connected to RP realms, so the old zones are pretty empty. Regular PvE realms connect probably every server to make a zone feel populated. It also doesn’t help that most level through repeated dungeon finder.
BfA zones feel populated with people running around with daily quests and farming getting people out in the world.