I'm being curious: What has declined on the WWII side since WWI came along (one month ago, btw) ?
Nothing. It's actually better than it was. This is a bit of gamer's ADD. I don't think of AH as a typical computer game but apparently it does attract members of that cohort.
Now, (prepare your flammenwerfer because I'm about to write YET SOMETHING ELSE that will get my butt crispy-fried - and this is serious) do I think the WWI arena was worth prioritizing, given the scarcity of HTC's precious development resources? Answer: I vote with my mouse and spend approximately zero time in the WWI arenas. I note that their popularity appears to have declined precipitously of late - and I qualify that as an anecdotal observation.
I'da rather had my 410 - but HTC already has me - bad, so, perhaps I'm not an at-risk customer and HTC made the right choice.
And I'll add, check the spelling on the subject. It's your first clue. Just sayin'...