Huh? Your answer surprises me, as I can think of tons of examples. Designers are often asked to provide a portfolio to show the work they are capable of. Same thing for photographers. In a previous life I was a ballet dancer, and the whole purpose of auditions is to demonstrate that you are a competent dancer.

I generally prefer an existing portfolio of code (e.g. github repos) to see the kind of code someone produces, but if you aren't able to show some fairly extensive examples of your work, homework is usually a bunch better assessment of your skills than what can be accomplished in a ~45 min interview.

Continuing: Imagine a guitarist wanted to join your band, but they refuse to let you hear them play until they're hired, saying they won't work for free.

Fair. I should've thought of designers and photographers. Ballet makes sense, since there are trials for prestigious orchestras and the like, but that isn't something I knew about.

When I wrote my comment, I was thinking of the medical profession, dentistry, auto & other mechanics, appliance and other device repair, construction ("there's a pile of lumber in the back, you have an hour to build a shed and then we'll consider hiring you"), plumbing, civil engineering ...

Most of those other professions you listed have much more meaningful and standardized certifications than software. A board certified cardiologist has already demonstrated real proficiency by going through the process to get certified. In software, the whole reason for these complicated hiring processes is that no one really trusts software certifications, and even company pedigree is not always a reliable signal.