It's the expectation that you need to demonstrate it at all, is the problem. How many lawyers sue people for fun so they can blog about it, how many doctors do surgery at home and stream "live cutting"?
We have created a treadmill that we can't step off
"software developer," as a label, doesn't signal that kind of credentialing (although something like advanced degree might), so our labor to differentiate ourselves goes elsewhere. i don't want to imply that this isn't a problem for our profession, but the amount of "wow we software engineers have it so difficult" sentiment in this thread seems high
A degree from a well-known school and a few years at one or more prestigious companies is an equivalent. Let's imagine a hypothetical developer who graduated from MIT then spent 3 years at Google. He or she would be as "credentialled" in the sense of the piece of paper opening doors as someone who'd gone the law school route and passed the Bar. That person will pass every resume-screen and get invited to an interview for the rest of their careers with just those two names listed.