In the UK at least there has been a strong drive to regulate security companies through organisations like CREST and CHECK. The problem is that its an industry with a massive amount of hidden information. If somebody does a pen test on an corporate network and says "we didn't find any vulnerabilities" how does a company know if they have actually done a thorough check or if the network is genuinely secure?
Yes in an ideal world we wouldn't need certifications or exams or anything but this isn't an ideal world.
