They key reason for juliaup is to make upgrading and parallel installs easy.
Outside some very special use cases, it makes sense to keep up with the stable releases or at least the LTS, as each new version brings a lot of benefits and performance improvements (and of course, potential bugs and regressions, but hopefully those are fixed quickly). juliaup makes this extremely easy, as you can just have julia point to the version you make default — you can change everything with a single control.
Similarly, users may find that they need an earlier version, or if they stick to LTS they want to test the latest release, etc. juliaup makes it trivially easy.
Last, but not least: you can also install nightly, beta, rc, and individual PRs. Yes, you read that right! You can do juliaup add prXXX and it will pull that image if available. This is like magic.
I am not sure what you mean by “deny” in this context. You can just write and release it. That’s how juliaup started. You don’t need approval from anyone.