I used to run one of the Huojin Pandaren Guilds when MoP came out. Every so often, I still log on to trial characters, trying to trick myself into thinking I have the time to dedicate to RPing.
While there are timeframes that make sense (WRA is a PST server, so don’t expect abundance of RP at 9 AM EST for example), each time I’ve logged in over the last year or two, I’ve noticed that WRA is generally… Far more empty.
While yes, there are individuals still in the Valley of Honor, there’s far less of a population actively RPing. It is almost like an idle simulator returning and checking in every 5-10 minutes to see a post. Beyond that, there’s almost a pressure to type out a 3.5 essay in response to what feels like everything.
By comparison, MG doesn’t seem to have that. There are varying degrees of style and types of RP, and if you’re not thriving well with someone, it’s easy to find another style.
I’ll be blunt: WRA’s RP community is extremely alienating, even when I’ve RPed on WoW for over 12 years. If you don’t comply with the groupthink of (Which I want to emphasize isn’t a bad thing) the RP community as a whole, you rarely find success here. Beyond that, if you’re an outsider, it’s hard to break into WRA, as most of the RP community has long-standing storylines they are already involved in, and unfortunately, as an outsider, you don’t typically fit into being written into the storylines.
MG is essentially the polar opposite of this, and in part, it’s likely because of the law of large numbers. Yes, you still have that exact situation on MG, but it isn’t every situation. You can casually log onto MG and RP a cheese vendor with a story paragraph and get RP pretty easily.
I don’t think this matter of Alliance is more appealing than Horde (though I’m sure it is a factor), but it’s also just based on the accessibility of RP by large, which just happens to be Alliance on MG.