Not to mention all those companies, you know, released other games during the time. Bethesda hasn't been working only on ES6 for more than a decade, they put out two titles since then, including an MMO funnily enough. Pretty bad one of course, but hey at least it released and I heard they patched it to be somewhat decent now.
WoW's a particularly terrible comparison too. It was developed in just about less than five years, from early 1999 to 2004. During which Blizzard released two massively acclaimed games and assorted expansions. And of course, when we say SC is up to 12 years of development almost, it is meant so far; the game isn't even close to being close to release too. Could hit the 20 year mark, we got no clue.