maybe you don't need them or want them, but some people seem to still want the separation. they can play in them with all prompts, but there's no reason not to keep them as separate memes since they provide separate things. a/b/o is a trope that covers something that has its own world dynamic, including altered genitals and pheromones and a social class status. in heat and in rut is just boiling things down to pheromones and biology and wanting to mate. not to mention that the a/b/o meme allows for more gen scenarios and the aspect of exploring the difference in social class and the in heat and rut memes are just about smut.

like it or not, they provide different things and there's no need to mash them up into one meme just because you don't see a difference in them.