Not having level 50 ops in group finder makes perfect sense for casual players.
Those players can enter those operations easily enough without group finder.
How does entering the operation have anything to do with getting a group for it? Your "logic" would imply there's no point in having a level 50 HM group finder, or indeed any group finder, because "players can enter those" "easily enough without group finder".
As long as the rewards are only the same Classic or Basic comms that the level 50-54 players get (i.e. the Ultimate comms reward for the Classic Operations weekly still requires hard mode), there doesn't appear to be any reason why the option should magically vanish from Group Finder the second people hit level 55.