Another (more pedestrian) reason for inducing regime changes, not only in Irak, but all over the ME, might have been the intent to put pressure on the Iranian regime and bait them into going ahead with their ("secret") nuclear program. Iranian IRGC generals had the impression that only a nuclear arsenal would protect them from foreign interference. The nuclear deal was supposed to run out in the mid 2020ies, I guess at the very least by then Iran would have declared itself to be a nuclear power, if not earlier due to maybe a staged incident that would have provided Iran with the excuse to break the deal.
This was a scheme to set up a "Sum of All Fears" scenario, decades in planning.