Because unlike in most actual engineering disciplines software developers generally aren't held particularly liable for the failures that their bad engineering

Because unlike in most actual engineering disciplines software developers generally aren't held particularly liable for the failures that their bad engineering causes, whereas people who build faulty bridges or airplanes don't have that luxury. Software has built a lot of modern toys but it still plays a relatively limited role in the world of atoms rather than bits, but I suspect the value of credentials is going to appreciate as that changes over the next few decades.