There's that, and there's also (from personal experience) an element of superhero bias (or bias overcompensation? I forget which way this one goes), where basically someone who does not have a certification but can code something optimally is de-facto superior to someone who does have a certification and codes the same thing just as optimally.

Additionally, there may be some reciprocate signaling involved; if I look for certified programmers, people will see mere certification as sufficient to get the job, which is not what I want - I want people who have the actual ability. Thus, I should hire people with ability but no certification, which signals that the certification is "useless" or "not what we're looking for" relative to other criteria.

This seems to even out to a reflective equilibrium where official certification is a net negative.