Why it this important? It's, well, not very. It's a bit of an in the weeds talk about how game worlds are constructed and how they work. It's nerdy and detailed. If you approach how games work casually, this is utterly nitpicky and unimportant -- just play what makes you happy. If, however, you're actually interested in how games do what they do, and what they incentivize, then it's very useful to recognize that gameworlds have absolutely nothing to do with the real world, but instead may contain what we think about the real world. Gravity does not exist in your game, but what you think about gravity may. This leads to a better understanding of how fiction works in game, what elements are necessary to maintain coherent, believable worlds and what may be elided entirely, and where the fiction causality determination needs to or may occur.
Fundamentally, I think that this discussion really revolves around whether a person thinks that causality needs to be determined prior to the mechanics or if it can be provided after you have your answer from the mechanics. Those saying that the mechanics need to be more "realistic" are the former camp -- fictional causes need to be fed into or be part of the mechanics engine to be germane. The mechanics then determine the outcome of this. The latter camp is comprised of those that say that the mechanics only need generate a predictable probability curve of success/failure/complication and that the fictional causality will be whatever explains that. In the end, both generate solid fiction, but far be it for me to actually say that the ends justify the means. The only point of saying that the ends are indistinguishable is to say that method of play doesn't really affect fictional integrity at all. It does, however, strongly affect how you enjoy playing.
So, then, to circle back to why care. For those of us actually interested in these things, we've recognized that this knowledge has improved our play by allowing us to better understand what it is we like about the games. And, of course, we like being nerdy about these things. The discussion is part of the enjoyment.