When does a thing stop being that thing.
A Genre is a broad term to try and classify. You start to create titles and classifiers and begin to find that many of those classifiers that you use to try and segregate can still be used in conjunction with another to classify something new. Look at games for example. There are very few games that have distinct classifiers that segregate themselves from other games.
Call of Duty: First Person Shooter, Online Multiplayer. Ok, not that hard. Does it have a story? It has a single player mode with a story, yes. Call of Duty: First Person Shooter, Online Multiplayer, Story-Based. Does it have Cooperative modes? Sometimes. Call of Duty: First Person Shooter, Online Multiplayer, Story-Based, Cooperative. What time era is this? This is largely fiction or non-fiction? Are all First Person Shooters like this? Are all Story-Based games First Person Shooters? Do all First Person Shooters have Cooperative play? We can actually keep adding onto the genre listing for a quite a bit.
And we have to keep making more and more qualifiers to describe a game because we can’t make assumptions about genres anymore, nor was it ever a good idea to start. It’s like trying to classify movies as either drama or comedy. For there to be tension, there needs to be drama and struggle, choice and impact. Action movies have drama. Sports movies have drama. Documentaries have drama. If a comedy didn’t have drama then it would literally be a movie with only stand-up. No, that’s not fair either because good stand-up, storytelling or joke telling, still builds tension and releases it conveying the drama of the situation. The only clear lines you can draw are ones like Animated or not, and even those have movies that blend the genres together like Heavy Metal (1981).