There is no good reason. Some colonel gets the individual training portfolio and figures he needs to change it all to fill out his PER. Perhaps his new way actually makes more sense, but what these people don't understand is that the act of change is often not worth the benefit, especially with name changes. The course content is basically identical with individual performance objectives being sometimes moved from one course to another. All the name changes in the world aren't going to change the fundamentals of training recruits.
GMT, TQ1, CLC made sense.
QL2, QL3, JLC made sense.
BMQ, SQ, DP1, PLQ makes sense.
But I wonder how much confusion has arisen from O Groups where guys making decisions have been out of the IT system for awhile and aren't up with this month's alphabet soup. I hope the rate of change slows considerably soon. Scheme A is good, Scheme B is good, the transition from A to B is the problem, and the people writing publications would do well to consider that.