One major reason those FAs are so worried about it is that there are part of the few but proud dedicated domestic 772 crews of FAs. (the vast majority of 772 crews are international, of course)

As we all know, the domestic flights on 772s have been dwindling rapidly. We're pretty much down to a JFK-MIA-JFK turn, ORD-DFW-ORD, and LAX-MIA-LAX. (Used to be a DFW-MIA and some other stuff IIRC.)

If DFW-ORD goes away or moves to LAX-MIA, those DFW-based domestic 772 FAs might have to start flying other aircraft regularly. There is particular concern that some of them might have to start flying the 757, which makes them shudder after the 772. The 772 is by far the most popular aircraft for FAs, hence why it is so senior and why the crews are so desperate to hang onto their domestic routes.