I like the fabric that is 65 threads per inch. 75 seems a little tight for quilt fabric. The higher weave possible takes the dyes better so that may be why the change for some of the lines, lots of different colors in the design or maybe different dyes are being used. The cloth cost more but maybe the new dye being used cost less. You'll never get a real straight answer to why, just the pros of why. I doubt the reps or employees or even the designer know unless they are in on the manufacturing cost decisions.