It’s pretty simple, Apple could decide not to approve the app, and
if they don’t approve it you can’t sell it. You can’t even give it
away. You don’t find out if you’ve been approved until the last
step, after you’ve fully invested, which you could lose, totally,
if Apple says no.
It’d be different if Apple had published an explicit rule stating, for example, that podcasting apps are prohibited. But there is no such guideline. Podcaster seems to fully comply with Apple’s published guidelines, and yet it was rejected for violating a secret rule.