You can't seriously compare 12-year old game, which graphics was obsolete before release with a modern game.
Of course I can! Just did! So did you.

It isn't an equal comparison, but it is a comparison.Pretty much. WoW does look really nice, and they've done a lot with it graphically over the years, even upping the system requirements at one time. But all in all, it's still an ancient game running on a 12 year old engine. Also, it's an MMO, which benefits immensely from toned down graphics. A giant, nearly seamless world and the ability to have dozens of player characters in small vicinity, as well as the need to appeal to a very wide market all influence the graphic quality. It's not really an equal comparison. I agree Blizzard deserves applause with what they've done with that tech; not because of a comparison to Civ or Firaxis.
Both companies have venerable game titles whose essential gameplay has not changed since their very beginning. Both companies have published improvements over the years. Both companies have been successful.
One company has chosen to constrain system requirements. The other company has chosen to use graphics that require new hardware for each release.
Neither company has needed to invest significantly in AI (yes, it's not real AI.)
So, comparison achieved.
I'm not saying that one company is right and the other is wrong; both games are successful. The different strategies are deliberate.
Of course, I do wish Civ hewed closer to Blizzard's model, since I find that simpler graphics usually enhances gameplay (on Galciv2, for example, I *always* used the ugly, strategic graphics rather than the pretty ones, because the former showed more information and was much easier to read). But that's just me.
Meanwhile, Blizzard has managed to continually refresh and improve WoW, despite retaining "ancient" code. Gotta admire that! (Ancient code under continual use also has the virtue of having been debugged.)
So Firaxis gets a "sigh, but I understand" while Blizzard gets a 21 gun salute.
Different genres? Not sure that matters here; for all I know, Civ might have done even better were development resources devoted to something other than eye candy, which is not what I suspect keeps the game successful. Of course, Firaxis has given this far more thought than I, so I am probably wrong.
Just as an aside, at release WoW minimum requirement was a 4 year old GPU. Civ VI minimum requirement is a 6 year old GPU. Also, at the time of WoW's release, a dedicated graphics card was required, no integrated graphics would run it at all, unlike Civ VI, where modern integrated graphics, like intel HD 5500, are likely to be able to run it. Though that is more related to intel improving the tech, but the point is, if you were on a laptop in 2004 with integrated graphics, you were SOL if you wanted to play WoW.
That's fair. But modern integrated graphics are not likely to run Civ7.
Anyway,
Ken