I would guess non-revs or something. I've never seen it though so not sure. The only time I really see Sundaes offered are on business, businessfirst, global first or PS flights, and the only domestic CPU eligible flight I've had one was to HI.

Being based in ORD I don't really fly many transcons so can't comment on that. I will tell you that from ORD-LAX or SFO I can't ever recall getting a Sundae. I did have one transcon last year (LAX-IAD), but my upgrade didn't clear so not sure if F got sundaes or not.

Now when ever flying BF on an int'l flight, I've always gotten a sundae and much to my surprise my last flight ORD-HNL we got sundaes as well!