Someday
Perhaps the reason why these people talking about their father or Rebbe who was Niftar instead of saying all the words you mentioned and only say ZT”L perhaps it’s because of Humility for their greatness of their father or Rebbe even if he’s no longer alive but they still want to keep their rebbe’s humility and simplicity instead of speaking out about all his greatness so they just keep it simple and say ZT”L
may all the Niftar we have lost in the past have an Aliya rather they we’re leading Gedolei Hador Worldwide or not. Maybe in truth in their simplicity and humility without being a leader in klal yisroel they really were great people staying simple and humble and running away from honor and respect.