The purpose of a journal is to be read, the purpose of a conference is to be heard, and they should be optimized for the desires of the audience, not the desire

The purpose of a journal is to be read, the purpose of a conference is to be heard, and they should be optimized for the desires of the audience, not the desires of the authors. A journal or conference that publishes everything is useless to its audience, which expects significant curation and filtering to pare down the incoming firehose to something that (a) fits a specific topic and (b) has a filter for quality and (c) pick the most interesting ones out of all the far-too-many decent papers that fit the first two criteria. There's no problem to publish them all somewhere, that's being done on e.g. arXiv, pretty much every recent useful CS paper is there as well, often before being published in a "proper venue" - but a "publish everything" service is not enough, people do want to read more selective sources instead of trying to skim everything that's posted on arXiv.