I'll consider the possibility that the engine is blameless when I see two Unreal Engine games that do it well, hinting that it's not unreasonably difficult. Sometimes a tool just doesn't work well for certain uses. That could be due to a design that tries and fails, or one that doesn't try at all and lacks a good foothold for a custom approach.

In any case, my comment is not about one specific issue. Thus the words "for example". The point is that what GGP said was obvious is in fact not obvious. Blizzard might very well have passed on that engine because of limitations they found, regardless of whether they detailed them publicly.