The official statement they'll make is that you aren't in CASS/non-rev til checkride, but in reality CASS enrollment and non-rev system enrollment can happen around when you hit sims.

It is also possible to cabin-only jumpseat prior to CASS processing, and I never had a problem with it on SWA starting the first wknd of class.

Essentially, they want to avoid dealing with ppl completely new to the concept of commuting and the complexities of cabin-only non-CASS jumpseating. And besides if it's someone's first 121 schooling they shouldn't be going home every wknd like some of us did.

If you are an experienced commuter who needs to get home just list SWA cabin-only (and do not under any circumstances get stuck).