While good stock fitters are few and far between, the reason is that people just won't pay them enough to do the job. What people don't understand is that once you find your measurements to fit one gun, its much easier to fit other guns to you, depending on the type and style of shooting being used.
I had a friend who left his LOP dimensions with a gunsmith over near Peoria, Illinois, and when he bought a New shotgun, he would drive over and drop the gun off at the gunsmith's shop to have the gunstock cut to his requirements before he even fired a shot from the gun. I was with him the day he picked a new Ljutic single barrel Trap gun, and went with him to the Peoria Skeet and Trap club where he shot the new gun for the first time. I believe he broke 48 out of 50 targets, with 23 on the first field, and 25 straight on the second. He began using that Ljutic for trapshooting thereafter, setting aside his other shotguns. He did have an old Model 31 Remington, and when I found a release trigger for it, and he put it in the gun, he took that out to shoot, again, for the first time in about 20 years. He had broken his first 100 straight targets with that gun, and only stopped shooting it after he needed to switch to a release trigger, and didn't have one for that gun. Of the more than 3 dozen shotguns he had in his gun collection, about 10 had been fitted to his dimensions. The others were "collectibles", that he only occasionally shot.
There is a good book out on gunstock fitting, the "Stock Fitter's Bible", By Rollin Oswald. The writing is a bit pedantic, but with excellent reason. The author is a skilled fitter, and he doesn't want the reader to skim the book, and miss important Step by Step instruction. If you read the book carefully, and then follow his instructions you will have a well fitted shotgun or rifle to shoot.
I have had stocks fitted to me by 4 different Smiths, and all pretty much followed the same methods to fit the stock to me. 2 of them have passed, but the other two are alive and still doing a bit of work for people who appreciate what they are doing.