To me, it matters because the use and reliance on LLMs demonstrably erodes cognitive capacity and ability, and submissions tainted by them should be subjected to an elevated level of scrutiny, which can only be facilitated with a consummate element of transparency. That elevated scrutiny could, and probably should, also be applied to non-LLM infected submissions, but doing so wouldn’t negate the labelling of authorship.
Good faith proponents of LLM assisted tooling should be in favour of overt transparency and labelling, as it’s a requirement to facilitate future historical analysis of their utility, efficacy, and legitimacy; you know, to build a body of evidence.