The Macross franchise, through most of its glory days, was defined by radical reinvention and continual shifts in tone and setting and music. Something I'm sure was done to protect himself from himself so he could go to sleep at night. But one thing I constantly hear from creative types is that once a person gets deep into middle age, their creative juices begin drying up. Frontier, to me, was already a big compromise with regards to Kawamori's originality decree. So much of that show and film series relies on straight up pastiche that it's almost suffocating at times. But at least it was like a DJ Remix rather than just a xerox copy. Delta however took things even further, and was basically just a Macross: Greatest Hits! Kawamori is already older than Hayao Miyazaki was when he made Princess Mononoke and Spirited Away, which was when he was first talking about how he was getting too old for this shit and looking to retire. So doing something easy and going back to the Frontier-well (which was probably the most profitable the franchise ever was) makes sense and fits the ongoing trends.