Mishpacha had a feature about R’ Chaim Kanievsky. To show how he was kulo Torah, a family member (I think it was a daughter) told the following story:
Once the Rebbitzin was not feeling well. R’ Chaim asked if he could do something for her. She asked for a hot tea. After waiting awhile, she asked if it was ready. Turns out, as it was the first time making tea, he did not light the fire under the kettle. She then explained to him in more detail how to make a tea. He did it, and when bringing it to her, dropped the cup. That was the last time she asked for his help in domestic matters.
For R’ Chaim, it is Torah only. For other gedolim, it may be different, and it may be different at different times in their lives. When their whole life revolves around learning or helping the klal, they don’t have time for other matters, and it is only appropriate for others to fill those needs- whether a family member or gabai. Imagine the president cooking his own dinner or going grocery shopping!