Why? I never used to. Until I did this. Now, I use them all the time and a pliers to manipulate hooks out of them. I have also heard that your hands brushing the slimy layer of stuff off the scaly side of the fish leaves it vulnerable to parasitic infections that can also kill the fish.
So whatever you do, if you have set the hook (in most cases hard enough to rip its head sideways in the water) then landed it (another fight as you rip it through weeds, over timber, through water as it thrashes about getting drug along by its mouth with big hooks jammed into its flesh to keep it coming your way) then flip it out of its environment into the air and onto your boat or into your hands or into a net, sounds to me like the fisherman has already given that fish a lot of "trauma" already. Getting the hook out and securing it with a plastic utensil is probably the LEAST brutal thing you are going to do to that fish while interacting with it, unless you put it in your live well and drive around all day keeping it in Fish jail.
I am not going to get too sentimental about God's precious creature when I set about handling it to get the hooks out and get it back in the water. I love bass FISHING, I don't worship "bass." That thing has survived everything else I just put it through to get it into my hands, it will survive a plastic grip in its mouth (which has to be a darn sight more pleasant than the HOOK I just set into it minutes or seconds before), it will make it through the last minute or two of me getting it released back into the water.
To me, the LMB is not an endangered species, it is a game fish, it kills without hesitation in its own environment, it is a predator in the food chain, it lives by the kill or be killed survival of the fittest mentality, so I'n not too hard pressed to treat it with kid gloves.
It's a bass, not a Faberge' egg.
Now I have zero tolerance for flippant disregard for the thing, or abusing it, or using it as a football for sport or whatever, but there are 100's of thousands more where the one I am currently holding with a gripper to remove a hook from its mouth without impaling myself came from, and its not made of fine spun sugar. It will live. And I doubt it will go off into the wild thinking "man, I didn't mind that big hook driven halfway through my skull, or that dragging me across the lake through the moss and over that log by my face, and even the getting hauled 6 feet into the air wasn't that bad, but those darn plastic grippers! Those things just irritate my jaw, that smooth plastic is like chalk on a chalkboard! Whey can't they just manhandle me with their big fat fingers squeezing me tight over my back scraping against my skin!?"
So anyway. That's my take on pampering the catch. No need to be cruel to the thing, but no need for kid gloves either. The best thing to me is to get it off the hook and back in the water as fast as possible. That is what that fish wants most of all. To be back in it's own environment and away from you. So if grippers make that a faster and smoother transition and enhances my safety from getting hooked again, then grippers it is.