oomis,
you are most certainly correct. HOWEVER, they (shadchanim) don’t feel comfortable doing so at the begining, and their lack of comfort level is to a large extent due to how they will be perceived if they were to do it.
in light of that, the question became, what can be done after the fact to tactfuly request shadchanus.
Perhaps this thread will assist in doing away with some faulty notions, and the day may yet come, when shadchanim are comfortable expressing up front what their shadchanus fee is, or some variation of that.
(btw the comparison to mechantanim would be if each time a boy and girl date, prior to date #1 the two sides would sit down and discuss financial arrangement should the couple get engaged. You can well understand that such would be uncomfortable in light of the reality the the overwhelming majority of first dates (it’s probably something like 1 out of 20 for the younger singles) do NOT result in engagement. As such shadchanim would feel silly talking about payment each time before a first date, since it is very unlikely to result in engagement. If the system was that shadchanim were paid date 2/ date 4, then i think it is more likely for such discussion to take place prior to date one.)