Probably because most of the time the big slop is coming from things like rod ends and ball joints. Maybe it was to caution against OVER tightening the sector mesh adjustment. It's pretty common for guys to do so because it's quick and dirty. You do NOT want to do that - overtightening it can accelerate wear, and possibly increase effort (because you've essentially used up all the operating clearances and you're wearing metal!) in an extreme case, and you'll wind up with MORE slop from the box in the end. Most recirculating ball boxes specify a given peak torque in inch-pounds, measured with the pitman disconnected in the vehicle - in that case you use a socket to connect the pointer-style torque wrench to the wheel retaining nut in the cab. Obviously you need to pull the horn pad for access, and you also need to disconnect the P.S. fluid line at the resrvoir, cap the reservoir, then put the return line end in a bucket and run the wheel back and forth several times to clear fluid. For the Ford integral power box, my 88 manual says you then rotate to the right until you're 45 degrees short of the right stop, then slowly rotate 1/8 turn back towards center and note the required torque. Now, turn back to center and record torque going back and forth across center, plus or minus 90 degrees. For any truck with more than 5000 miles on it, the spec value is 10-14 inch lbs more effort going over center than you recorded over near the right stop, with adjustment recommended only if you're showing LESS than 7 in-lbs difference. Doing this last is smart - you may not need adjustment. With a little help and some leverage, you can measure play in other front end components and the majority of the time, THAT is where you'll find your problems.
