Hi Steelheadman: You asked "why do they call them float rods" The short reply is that they are designed for float fishing,primarily with a centerpin reel.
Usually a true float rod is 12 to 14 feet in length so you can easily hold all line free of the water out to about 75 feet. Casting with a centerpin is different from casting with either spinning reels or baitcasters. The cast is a more sweeping action without any tip snap. The float rod is therefore firmer in the tip and softer in the butt. Somewhat surprisingly a 12 or 14 ft traditional speycaster rod in 9wt makes a very good centerpin rod.
The centerpin rod also has a different placement of the reel seat midway between the placement of a fly reel with a fighting butt and a baitcaster butt.
There are very few factory built centerpin float rods.I believe that Talon makes them in a 13ft 2 piece configuration and Loomis used to make a 12 ft model.
coot