Sewall,
Good question and I applaud you for asking "why" versus accepting the status quo. My suggestion would be for you to do your own research and come to your own conclusion. I think you may find some emotion around this topic because of its historical tradition - my (dad, granddad, mentor, old rancher down the road, ___ fill in the blank) did it this way.
Here's my conclusion from the research I have done:
For the typical cow/calf producer: No Value. 2005 article by G. Bretschneider from Unv. of Nebraska: "ADG of bulls increase up to 19% than that of steers". Though I have seen some studies suggesting bulls get docked; no where have I been able to find the % docked approach anywhere near this type weight gain difference. Also, the producer assume the cost of labor, medication, risk of loss, etc. Lose 1 of 100 calves to blood poisoning or some other complication and any premimum for a steer quickly disappears.
Packer: Value. a study from Roman L. Hruska U.S. Meat Animal Research Center, ARS, USDA, Clay Center, NE and several others concluded the marbeling is better and higher grading. Thus, the packer can charge more for his product but assumes none of the above risk and expense the producer does.
Consumer: No Value. The same study above from Clay Center concluded, "Meat from bulls had higher (P < .05) shear force values than meat from steers; however, sensory panelists were unable (P > .05) to detect differences in tenderness or other sensory traits between bulls and steers". Thus, the consumer pays more for a product that they cannot detect any difference in and thus their eating experience is the same.
I think PB breeders on the other hand have a different incentive in improving the breed. Also, please note nowhere do I suggest the breeding of inferior bulls. The above conclusion is for a typical cow/calf producer that sells their calves at weaning.
Again, this is only my opinion base on the research I have been able to optain. I suggest you research for yourself.
Good Luck.