There are a number of dilemmas organizations face when considering internal audits:
The organization can be very small, and as such, how do they ensure that (when everyone has a hand in nearly everything) you don't audit your own work? (Why did TC 176 remove it? Feedback from mainly small organizations?)
With organizations which are new to Quality Management, even if they send someone to a course, how do they ensure effective audits out of the chute. Class simply makes new internal auditors "dangerous"...
Contracting internal audits can be an option, but the contractor might just do audits like a CB auditor (I've seen this soooo many times, it's scary) and bring little to no value.
When much of the available auditor training simply replicates the external audit model, which CB auditors love (because they usually ONLY see audits and requirements that way) the client doesn't get the deep dive on their Quality related/Operational issues which need bringing to the surface because the internal person is using the wrong tools...
Until the powers that be (ISO 19011 writers, IRCA, Exemplar Global etc) recognize that there's a HUGE difference between effective internal audits, vs external audits, this confusion will reign.