Some might forget, some might simply become convinced that the new variants are inherently superior, so they have no need to make the close-minded trinkets of the past.
I mean, they certainly can do what you say, I just think it'd be much less common an occurrence.
I can accept its a less common occurrence, it's when people are adamant its an impossibility is laughable. Too much typecasting, especially for CSM where its possible for different outcomes for CSM because they have less rules and dogma. I bet you most traitors would have stayed in real space if they didn't get kicked into EoT in scouring. New lore has busted them outta there, its possible to re-arm, rebuild etc. Not everyone is going to be weak still like the NL force under Talos etc. Realspace offers a chance to weak CSM forces to grow and thrive again, more so now post Cadia.