I did a quick search on Linkedin to compare the number of user profiles listing each of the major IT certifications. This is just a rough sampling, as not everyone is on Linkedin, and not everyone will list their certifications, or spell them correctly, and there is overlap between the groups when someone has multiple certifications, but it gives a good overview of what is popular.
Surprisingly, ITIL, PMP, and PRINCE2 came out ahead of Microsoft, Cisco, and Oracle, but CISSP, CISA, and CISM are rising fast.
If you consider that each of these certifications cost between $250 (average exam cost?) and $10000 (multiple weeks of training plus exams) then it is easy to see that there are billions of dollars being spent every year on certification. 20 years ago there were no certifications, and employers just asked a few technical questions during the interview ...