I think its because a very large percentage of CEs work in consulting firms. Perhaps that is the main means of employment for them- as opposed to MEs working in factories, controls contracting firms, mechanical contracting firms, etc...
Consulting firms look up to PE licenses. Since CEs mainly work in firms, many of them go after the PE.
I really never had anyone care that I went after my PE license except for the times I worked in consulting firms.
This is just my hunch.
Ed