I guess think of it like religion. There's no logical reason behind religion... but it exists. It's more of a cultural phenomena then a strategic action.
The people who believe in the religion can't differentiate between religion and truth. Hence if a huge number of people in a company believe it as truth, it becomes part of company policy.
In addition to this, many occupations over time develop standardized testing and filters to keep supply low. Keeping supply low is a logical incentive but there's no one guy who set the policy to be this way with the purpose of creating a cartel. Much of this happens organically as cultural phenomena. Doctors and lawyers are good examples of this.
Training to become either a doctor or a lawyer is actually quite excessive and there's no proof that the people who make it through these gateways are better performers. In fact, there's statistical proof that doctors in the US who go through one of the hardest filters ever to become a doctor are actually much less effective then their European counterparts. This indicates that the filters don't exist because they create more effective doctors.
I think software is going through a similar process. It won't get encoded into government accreditation. But it will be used by elite companies to form the typical class based social hierarchy which is a cultural phenomena that forms across every single culture.