If there's more good papers due to more activity, doesn't that allow for the possibility of more conferences and journals to publish to, which increases the acceptance rate?
I don't think that the solution has to be that existing conferences and journals accept more.
The problem is that external environment (namely hiring) creates pressure to publish in a handful of prestigious venues. Nobody wants to be the odd one out that has their papers in some less well known conferences.
There could be more top-tier conferences, though. If the field grows, it makes perfect sense for the number of top-tier venues to grow as well (for whatever percentile we set as a threshold to be "top-tier"). And creating more venues is also good for people who might not have funding for long trips across continents (although lately, accommodation costs tend to be increasingly dominant with respect to flight costs in most destinations I'm traveling to).
In general you're right, but I believe that there are ways to do it. For example, if an existing top tier conference split into several (e.g. say that NeurIPS decides to hold 3 conferences a year, NeurIPS-America, NeurIPS-Europe and NeurIPS-Asia, or whatever) in practice they would probably be top tier from the get go.
Many research organizations use formal conference/journal rankings. These are usually calculated by following h-index values for papers published there. A new conference would start as unclassified for a few years and could not be used when you need to hit some formal criteria in academia.
I don't think that the solution has to be that existing conferences and journals accept more.