ChemRxiv vs. arXiv acceptance
The main problem is that your impressions seem to be incorrect. (At least from my maths perspective) Putting a preprint on arxiv is just that, namely putting up a preprint. Almost everything put on arxiv will be sent of to a peer reviewed venue as well, usually at the same time (there are exceptions, e.g. when people put up non-articles such as lecture notes for posterity). It is useful to make a result widely available and in cases even to establish priority, but it is not "proper" publishing and generally is not accepted as such. It is just a way to put the result out there right now instead of waiting until it is published (which in cases can take years). 

In a way this approach is an attempt to please both sides. The bean-counters and bureaucrats who care about numerical "publication record" generally ignore arxiv and look at peer reviewed stuff only. But the actual peers reading your papers care more about the content than about the venue it is published in. (Though they still will cite the published version if available)

Also keep in mind that people can only cite what they actually know about. And in some disciplines, the use of arxiv is so prevalent that it also functions as a unified source. Since every preprint is on there anyway, many people only check the new releases on arxiv, so not releasing a preprint is not an option anymore.