C.E. Evans wrote:
It really is as simple that it was just a change that Starfleet underwent during that time. I don't think Starfleet is a monolithic entity, but one that undergoes constant change for various reasons (pick one--social, political, or just for the heck of it). Some of these changes will sit well with some, but not with others.
That's on the level of "a wizard did it." Organizations comparable to Starfleet do not historically make comparable changes "just for the heck of it." Was there a social, political or cultural revolution in the Federation between TMP and TWOK? Maybe, but it doesn't seem manifest in any other aspect of the world we see.