I read somewhere (and can’t seem to find the link) that the rollback to the VAB is because there is a small battery powering the abort system that has an approximate 3 week lifespan. And this past sat was near the end of that timeframe.
The first is as you say, there's a timeline constraint based on the launch abort battery. It's previously been stated that NASA could attempt to get a waiver for the timeline.
But second reason is that the number of remedial and inspection actions you can perform on the launch pad is obviously more limited than in the VAB. Given that NASA did try for an immediate relaunch, it's likely that they've already tried and exhausted their highest value launchpad inspection and remedial actions.
- "At issue is the flight termination system, which is powered independently of the rocket, with batteries rated for 25 days. NASA would need to extend that battery rating to about 40 days. The space agency is expected to have those discussions with range officials soon."
- "If the rocket is rolled back to the Vehicle Assembly Building, which would be necessary to service the flight termination system or perform more than cursory work at the launch pad, NASA has another Artemis I launch opportunity from October 17 to October 31."
https://arstechnica.com/science/2022/09/years-after-shuttle-...
However, my understanding is that the current rollback is needed to address the hydrogen leak; they are not (quite) yet at the end of the rated battery lifetime.