They do care; Apple has shut down (or restricted) several apps over the years that have tried this. But I ultimately agree with you, it's really more about how it's presented rather than how it works under the hood. This might have a lot to do with the review process.
The subject we're talking about here would not fly under their radar.
What you're saying is that Apple is inconsistent in enforcing its officially stated policy. That may be true, but does not change what the official policy is and that they can enforce it any time they want to.
Apple does not care. As long as you are operating in the spirit of their App Store.
You know when they care? When you start charging money for those downloads. Via an alternative payment channel. Or when you run an alternative app store from within your app.
If you download assets on demand, and some of those turn out to be executable* code, nobody cares.
* Where executable means 'interpreted' because you cannot run unsigned code. But for games that is fine, they have been doing this with JS, Lua and Python for a decade.
(You can downvote me - but this is based on a decade of experience)