Could be that Paramount know there were fan groups based on "Starfleet Marines" since the 1970's and did not want to use the same name for the M.A.C.O.s possible copy right issues and what not.
Why? Paramount at the time owned Star Trek
lock, stock, and barrel. Anyone operating any Star Trek
-based club or business without a license from Paramount was technically violating Paramount's copyright. Paramount would have no legal obligation whatsoever towards them.