In harder content, you can't just move however you please all the time due to mechanics requiring more precise positioning from everyone. That means if you want to maximize your positionals as a melee DPS, you often need to take them into account while planning your movement and rotation, the tanks need to take them into account while positioning the boss and the group needs to take them into account while planning the strats.
No, removing positionals wouldn't completely cut movement, rotation, positioning and strat planning, but it would remove some depth from them, which many of us consider a loss. It's the same with any other aspect of the game and positionals play a part in many of these aspects. If you remove a part of something, you take away some of the depth with it, which in turn makes it less engaging to many.
Besides, if you don't even do content where dps matters, I don't see why would you be so turned off by positionals being required for best performance - it's not like they will matter at all in the content which you do. You can play a melee while ignoring positionals and perform well enough to clear in any dungeon or normal/alliance raid, even in extremes.