Well, because your walking foot probably shouldn't wear a groove into the metal parts of your sewing machine like this.
Ohhhh, so many curse words.
You see, I bought this foot several years ago (maybe 5?) when I made my first and only other quilt. Like you do, I just went to a local Joann's, bought the walking foot they had on the rack, and hooked it up to my machine. It screwed right in, and I thought nothing of it.
Fast forward to recently, and I ran into a situation that should have been a sign...but I totally missed it. I wanted to buy some more empty bobbins, and again, I just went to the local Joann's, picked up a multipack, wound one up, and immediately got frustrated when it just didn't seem to fit quite right. I compared it to one of my other bobbins, and noticed it was quite a bit taller. Huh, I thought. Ok. So I exchanged it for the other size bobbin pack at Joann's, wound THAT up, and while it fit better, it still wasn't an exact fit, and the bobbin jammed up and made a mess. I untangled it, and went back to return the second pack. This time I asked the lady working the sewing machine corner what was up. She informed me that they only sell accessories for Simplicity and Husqvarna sewing machines. I have a Brother. Still, no lightbulb moment for me.
I am finally to the quilting it all together point on my hand pieced quilt, and I was swimming along just fine with sort of straight line quilting, sort of an inch apart....when all of a sudden my walking foot just stopped walking. I was confused. The bobbin hadn't run out, the needle was threaded...what gives. I remained confused for a while, re-threaded the whole works, got through another couple inches, and again, it just stopped! This time the little arm thing fell off the screw thing it was (apparently) eating away...but I still didn't see that. I removed and reinstalled the foot, tried again, and again, the arm thing immediately fell off the screw thing.
That's when I noticed the groove that probably shouldn't be there. That's when I flashed back to the bobbin situation....and THAT'S when I figured out that, huh, that walking foot probably isn't a universal accessory.
Sure enough, they sell a specific walking foot to attach to my specific brand and model of sewing machine, and I am a moron.
I have since ordered that specific foot, and am avoiding actually trying it out because I'm afraid that I wore the screw thing away too far and that it won't work and I'll have to buy a new machine if I want to continue using a walking foot. This bums me out because first, the rest of the machine still works just fine. Regular presser feet don't rely on that screw thing, and the screw thing still holds the needle in as it's supposed to. Second, I have absolutely no idea what machine I'd want or need, and there are so many options out there that I feel overwhelmed by the variety and potential cost of replacing my otherwise functional machine.
So stupid. Use parts made for your machine. In this case....brand matters. Or at least MATCHING brands matters!