It is funny that you would say, one one hand, that it has no mechanical value, and then in the same paragraph you include the most upfront mechanical value per 3.5 RAW. The upfront mechanical value is that it makes money.
However, the 3.5 RAW also allows you to "use the tools of your trade, [know] how to perform the profession’s daily tasks, how to supervise helpers, and how to handle common problems." So, while these things may not be of obvious and immediate mechanical value, it is incorrect to imagine that they are without mechanical value whenever such a task applies. By RAW, Profession does something besides make money for a week's worth of labour.
It may be easier to see when Climb or Ride might apply; I assure you that many games have made Profession apply per RAW.
Here's another way to look at it. Your argument is, essentially, that Profession is too narrow a skillset to be valuable in game, meanwhile
Too narrow for some, too broad for others, and just right for still others. I hope you can see that this is very much a playstyle issue. Like, for that matter, so many other RPG issues.
RC