Probably because they are done with newhire classes for the year, so 717B on the AE would just remain unfilled. I would expect them to be present on the December AE though for the January newhires to fill.

In all the time I've been here (which isn't all that long), I've never tracked anyone who moved to 717B from another category (other than a base swap), though it's possible I missed one. And if it did/does happen, it's probably only to break a newhire seat lock after the first year to get to a desired base.

It's actually an interesting conundrum. If Delta were to stop hiring altogether, I'm not sure how they'd keep 717B staffed without doing VD or MDs.