Because.......that's the way we used to do it on the Tristar!
When I was on the Tristar, I was told it was because "that's the way we used to do it
on the Convair".
At least these days you don't, prior to ToD, have to state the readouts of all your primary flight instruments incl. ADI ("two-and-a-half degree nose up, wings level"). That on an aeroplane with an instrument comparator and a thingy monitoring the comparator too!
Unnecessary callouts..it has been thus for 30+ yrs.