That sort of delay can kill a new product's momentum. I wonder if this is consistent with what others have seen or if it's something unique to this project?
My app was nonsensically rejected for not having enough users yet. Isn't the whole point of the marketplace to help obtain users? When I replied to appeal (directly quoting the no-minimum-user-count statement), I never received a response, and none of the ~dozen GitHub employees I know were either willing or able to help me.
I gave up on the marketplace and just wrote my own Stripe billing, but after two years my app still only barely breaks even on its infrastructure costs. I deeply regret wasting my time building a GitHub app.
Adding insult to injury: my GitHub app is a SaaS CI version of my open source CLI tool, which GitHub internally uses as a core infrastructure component for their DB schema management. 8 months after my GitHub app's launch, GitHub open sourced some Actions code which uses my open source CLI tool to substantially duplicate the purpose of my SaaS app, albeit in a less compelling way (their approach doesn't provide inline annotations, is much slower to execute, and involves contorting the CLI in unintended ways).
Now I keep getting support requests from random users who want help configuring GitHub's action, but don't want to consider ever paying for a simpler-to-install solution with more features. It's extremely demotivating.
Based on my research I wouldn't recommend using GitHub Marketplace in its current state.
I've spoken to a few other GitHub app creators, it's a fairly common experience. I think GitHub Actions are kind of viewed as the preferred alternative by GitHub so that's what they're focusing on.