The new series have given us a few possible explanations for that.Isn't it also weird that Starfleet didn't change its uniforms for 40 years, then suddenly started introducing a new uniform style every eight years or so?
Actually Deep Space Nine was the first, showing the TNG uniforms still in use alongside the new DS9 uniforms. They could've introduced a new uniform style every eight years throughout the Lost Era, and kept the Monster Maroons around for postings that suited a more traditional look.
Picard showed that uniform styles can return after a gap, with its late 24th century look being very similar to the DS9 uniform. Maybe the Monster Maroons went away for a few decades and came back.
And Lower Decks showed that some places just hold onto old uniforms forever, while everyone else moves on.