The assets still need to be looked for, not to mention they're at-least made by human people. Those other assets also need to have any licenses or conditions followed, such as payment, attribution, whatever. Plus we're heavily encouraging doing as much yourself as possible. If we completely banned any and all outside assets, it would block the use of stock sound effect, font and texture libraries, a dealbreaker for 99% of people. Seeing as we're allowing teams, people who are missing the skills needed for certain aspects can always team up with people who do have those skills, so really we're giving as little reason to use more than a couple outside assets as possible here.
Now seeing as you supposedly don't plan on using AI in your own submission, I don't see why you insist on wasting both yours and my time nitpicking the asset rules. If "don't use a bunch of AI-generated trash in your game" is too big of an ask for someone, they shouldn't be joining a game jam, they should be watching some tutorials and learning some actual creative skills. I already changed the rule to be more lenient than I'd ideally like, I'm not changing it again.