Another dumb, pointless, speculative explanation.
Let me get this straight, we explicitly see Starfleet use 2 uniforms concurrently in multiple eras, and you have a problem with that because the Starfleet Quartermaster never shows up onscreen to lecture us on uniform logistics?


) and the military doesn't have one design of uniform for all officers and enlisted personnel no matter their jobs or ranks. Starfleet's no different.