The same reason all police procedurals get the procedure deliberately wrong, despite an even greater demographic group (veteran police and
veteran criminals) being able to tell the difference?
Realism is anathema to drama in too many cases. And nobody wants to watch real life when they tune in for entertainment. They want something better.
The uniforms and weapons were different too and showed that they were trained to provide military support above Lt. Reeds ship security forces.
Don't you mean below
Reed's forces? Note that the guns of the MACO contingent were of a supposedly outdated type. The MACO sidearm was replaced by the more modern phaser sidearm aboard Archer's ship in the very pilot episode, say.