Starfleet needs more variations not one uniform for decades.
I agree completely. The use of the monster maroons in TNG flashback scenes, Yesterday's Enterprise, etc. was done because of budget limitations of the time, not because someone felt a particular affinity for that uniform or made a conscious decision to have it be used for 70 years straight. Back when TNG first premiered, the now-unofficial FASA Officer's Manual had two 'intermediate' uniforms from the post-TMP films-pre-TNG era. That was more believable than reusing the maroons.