The players probably get told at their exit interview, but the club doesn't make any public announcements until after trade week is done and dusted.Not anymore. I was at the Royal Show when I found out Smack and someone else had been delisted.
The thinking seems to be that they might be able to trade them and get something in return, whereas players who have already been announced as being delisted can get picked up as DFAs and the club gets nothing.